Rhodium(I) complexes containing a bulky pyridinyl N-heterocyclic carbene ligand: Preparation and reactivity

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Rhodium(I) complexes containing a bulky pyridinyl N-heterocyclic

carbene ligand: Preparation and reactivity

Chao-Yu Wang, Yi-Hong Liu, Shei-Ming Peng, Shiuh-Tzung Liu

*

Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, ROC Received 25 March 2006; received in revised form 1 June 2006; accepted 2 June 2006

Available online 15 June 2006

Abstract

Coordination chemistry of a new pyridine imidazole-2-ylidene ligand (pyNC) system with sterically hindered substituents toward rhodium(I) metal ions has been investigated. The rhodium complex [(pyNC)RhCl(COD)] (COD = 1,5-cyclooctadiene) was prepared via the transmetallation from the silver complex [(C-pyNC)2Ag]AgI2. Upon the abstraction of chloride, the pyridinyl nitrogen

coordi-nated to the metal center and formed [(C,N-pyNC)Rh(COD)]BF4with the chelation of pyNC. The pyridinyl nitrogen donor was found

to be labile and could be replaced by various donors such as phosphine, azide and halides. Substitution of COD by various donors does not proceed except strong p-acid ligands such as CO and P(OCH3)3. However, the chelation of pyNC was replaced by the bisphosphine

(PP) to form [(PP)2Rh]BF4, which was subsequently oxidized to yield [(PP)2Rh(O2)]BF4.

Keywords: Carbene; Rhodium; Substitution; Coordination

1. Introduction

Since the stable diaminocarbene was ﬁrst isolated by Arduengo[1], the chemistry involving this type of carbenes has been attracted considerable attention [2–13]. These carbenes are considered as an important class of ligands with strong basicity and good r-donating properties. Thus, transition metal complexes containing N-heterocylic car-bene moiety were found to be thermally stable and less sen-sitive toward dioxygen as compared to those with phosphine ligands[7].

Regarding chelate-carbene ligands, quite a few hetero-functionalized diaminocarbene ligands are known [10– 12]. Amongst, Cavell and coworkers have demonstrated that the chelation eﬀect of the pyridinyl imidazole-2-yli-dene ligand 1 toward palladium ions is due to the pres-ence of a strong coordinating pyridinyl donor [9].

Furthermore, the carbene ligand with a steric bulky sub-stituent on the imidazole ring makes the coordination environment more versatile[9,10]. It has been shown that Rh(I) complexes with a bulky carbene moiety underwent C–H activation on the substituent of ligand itself to form a Rh(III) species[9]. However, bidentate ligands with ste-rically hindered groups on both pyridine and imidazole rings such as 2 have less examined [9]. In view of these background, studies on the synthesis of pyridinyl-carbene precursor 3, preparation of the corresponding rhodium complexes and their reactivities toward various donors were investigated. N R' N N C: R' 2 Mes= 2, 4,6-trimethylphenyl N N N C: R 1 N Mes N N Mes 3 Br R' : bulky substituents

*

Corresponding author. Tel.: +886 2 2366 0352; fax: +886 2 2363 6359. E-mail address:[email protected](S.-T. Liu).

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2. Results and discussion

2.1. Synthesis of ligands and silver complexes

The synthetic approach leading to pyridinyl-imidazo-lium salt 3 is shown inScheme 1. Mesityl substituted pyr-idine-aldehyde 4 was prepared in 90% yield from the coupling of mesitylboronic acid with 6-bromopyridine-2-carbaldehyde in the presence of Pd(PPh3)4as the catalyst.

Subsequent functional groups transformation provided the desired imidazolium salt 3 with mesityl substituents. The imidazolium salt 3 as well as the intermediates leading to it were characterized by both spectroscopic and elemen-tal analyses.

Deprotonation of imidazolium salt 3 with n-BuLi to produce the corresponding carbene (denoted as pyNC) did not succeed presumably due to the interference of the deprotonation of benzylic methylene protons[9]. Alterna-tively the carbene transfer method was employed to pre-pare the desired metal complexes (Scheme 2) [8,14]. First the imidazolium salt 3 was converted into the silver carbene complex 5[15]. In comparison with the related species, this

reaction took much longer reaction time for completion, indicating that the bulky substituents readily slowed down the formation of carbene complexes. Characterization of this silver carbene complex was based on both spectro-scopic data and elemental analysis. 13C{1H} NMR spec-trum of the silver complex showed a characteristic shift for Ag–C(carbene) at d 183.5, which was assigned to the

2C-imidazol-2-ylidene(carbene) carbon [16]. From the observation of m/z = 897.4 (107Ag) and 899.5 (109Ag) on the FABMass spectrum clearly illustrated the formation of Ag(I) bis(carbene) complex, which had the same stoichi-ometry as those reported species [15]. Elemental analysis of the complex also suggested the formula of (C-py NC)2Ag AgI2, but the crystallization of the complex in

CH2Cl2/hexane gave the X-ray suitable crystals in the

for-mula of (C-pyNC)2AgI, a substitution of [AgI2] by the

iodide anion.

Fig. 1 displays the ORTEP plot of the silver carbene

complex (C-pyNC)2AgI. The angle of C(1)–Ag–C(28)

[160.7(2)] is much deviated from the linear geometry, which is smaller than those of the reported species such as [1,3-dimesityl(imidazol-2-ylidene)]2Ag+ [176.3(2)] [15]. N Br CHO B(OH)₂ Pd(PPh3)4, Na₂CO₃Ar' N CHO Ar' = 2,4,6-trimethylphenyl 1. NaBH4 2. PBr₃, 3. ImAr' _Ar' _N N N Ar' Br 4 6

Scheme 1. Ligand preparation.

Ag2O, NaI N Ar' N N Ar' Ag..AgI₂ N Rh N Ar' N Ar' BF4 AgBF4 [Rh(COD)Cl]2 N Ar' N N Ar' Rh(COD)Cl Ar' = mesityl 2 (COD) 3 5 6 7

Scheme 2. Preparation of rhodium carbene complexes.

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The angle between the two planes, deﬁned by two imidazol-2-ylidene rings, is 77.07, whereas the dihedral angles formed between the plane of the picolyl and imidazol-2-yli-dene rings are 77.62 and 76.66, respectively. These obser-vations might be a result from the relief of the steric interaction of the bulky substituents. Distances of Ag–C are 2.108(4) and 2.117(4) A˚ , similar to those of related spe-cies. All other bond lengths and angles are expected. 2.2. Rhodium carbene complexes

Treatment of [Rh(COD)Cl]2 with silver carbene

com-plex 5 in dichloromethane at ambient temperature gave the desired rhodium complex 6 as yellow crystalline solids in quantitative yield (Scheme 2). The structure of this rho-dium complex was determined by both spectroscopic and X-ray crystal structural analyses. A signal of doublet at 182.0 (JRh–C= 51 Hz) on the

13

C{1H} NMR spectrum is assigned as the Rh–Ccarbene resonance, indicating the

suc-cess of carbene transfer from Ag to Rh. The methylene lin-ker between imidazole and pyridine rings exhibited two sets of doublet at 6.39 and 5.92 with the coupling constant of 14.8 Hz, showing two non-equivalent natures of these pro-tons. In addition the ortho-positioned methyl groups on the phenyl ring are magnetically non-equivalent, resulting from the hindered rotation of the methylene unit caused by the bulky substituents and ligands.

ORTEP plot of 6 is shown inFig. 2. Molecular geome-try around the metal ion was in square planar arrangement with two coordination sites occupied by carbene and chlo-ride. It is quite clear that the pyridinyl nitrogen donor remains uncoordinated. The average distances of Rh– C(COD) trans to carbene donor [2.18 A˚ ] appears to be

longer than those in cis arrangement [2.10 A˚ ], suggesting that the r-donor character of the diaminocarbene is stron-ger than that of chloride. No major deviation was observed in bond lengths (Table 1). It is noticed that the imidazol-2-ylidene ring is bisected with the coordination plane by ca. 63.6.

Abstraction of chloride from complex 6 via the addition of silver ion readily assisted the coordination of pyridinyl-nitrogen to the rhodium center, allowing the pyNC to form a chelation (Scheme 2).1H NMR signals correspond-ing to pyridinyl hydrogens of 7 shifted downfield by ca. 0.4 ppm. This coordination chemical shift gave an indica-tion of the coordinaindica-tion of pyridinyl-N donor toward metal center. However, the conclusive confirmation came from X-ray single crystal determination (Fig. 3). Similar to those rhodium complexes, the metal center in 7 again displays a square planar geometry. Bond length of Rh–N [2.223(3) A˚ ] is in the normal range. Notable feature of this structure is a difference of 25 between the angle of Rh(1)–C(9)–N(1) [141.0(3)] and Rh(1)–C(9)–N(2) [115.6(3)], presumably due to the constrain raised from the chelation of PyNC. The bisect angle of imidazole ring and rhodium coordina-tion plane is 49.9, which is smaller than that in 6. 2.3. Reactivity of rhodium complexes

In order to understand the nature of the pyridinyl carbene bidentate, substitution reactions at the rhodium center with various ligands including r-donor and p-accep-tor ligands were examined.

Table 1

Selected bond lengths (A˚ ) and bond angles ()

Complex 6, X = Cl(1) 7, X = N(3) 8, X = N(4) 9, X = N(3) Rh(1)–C(1) 2.045(2) 2.044(4) 2.038(3) 2.051(4) Rh(1)–X 2.3942(6) 2.223(3) 2.180(3) 2.160(3) C(1)–N(1) 1.367(3) 1.371(6) 1.363(3) 1.355(5) C(1)–N(2) 1.358(3) 1.33(6) 1.357(3) 1.351(5) Rh(1)–C(28) 2.185(3) 2.202(4) 2.178(3) 1.919(5) Rh(1)–C(29) 2.172(3) 2.241(4) 2.198(3) 1.828(5) Rh(1)–C(1)–N(1) 130.0(2) 141.0(3) 131.4(2) 137.1(3) Rh(1)–C(1)–N(2) 126.5(2) 115.6(3) 125.1(2) 118.4(3) C(1)–Rh(1)–N(3) – 84.5(1) – 87.2(1) C(1)–Rh(1)–X 90.75(6) – 90.8(1) –

Fig. 2. Molecular structure of rhodium carbene complex 6 (30% proba-bility ellipsoids).

Fig. 3. ORTEP drawing of cationic part of complex 7 (30% probability ellipsoids).

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2.3.1. Azide

While complex 6 reacted with excess amount of sodium azide in reﬂuxing EtOH/H2O, chloride was replaced by

azide anion to form complex 8 (Scheme 3). Similarly, reac-tion of 7 with equimolar amount of sodium azide in dichlo-romethane yielded complex 8 as well. 1H NMR of this resulting complex was quite similar to that of 6. Infrared spectrum of the complex showed a characteristic absorp-tion at 2038 cm1, which is typical for the coordinating azido ligand. Still, the molecular structure of this azide complex was unambiguously proved by X-ray single crystal analysis (Fig. 4). Complex 8 appears to be in square-planar coordination geometry around the metal center with all bond angles and lengths in typical ranges. Bond length of Rh(1)–C(9) [2.038(3) A˚ ] was slightly shorter than that of complex 6. As for the bond lengths of N–N of the azido ligand are in a diﬀerence of about 0.15 A˚ , which is quite diﬀerent from those reported terminal azido rhodium com-plexes[16].

This azido rhodium complex proves to be thermally sta-ble and insensitive toward moisture and air. It even remains intact by UV irradiation (254 nm) at 60 C for 12 h. However, the azido moiety readily underwent the ligand transfer from rhodium center to the other metal ion when complex 8 was treated with a THF solution of [(COD)RhCl]2 or [RuCl2(p-cymene)]2. In both instances,

the chloro-rhodium 6 was obtained accompanied with the formation of [(COD)Rh(l-N3)]2 or [RuCl(l-N3

)(p-cym-ene)]2, respectively. The replacement of the

pyridinyl-nitro-gen by azide shows the hemi-labile nature this donor, which is also found in the treatment of complex 7 with chloride. Thus, reaction of 7 with excess of tetraethylam-monium chloride yielded complex 6 quantitatively. 2.3.2. Carbon monoxide

Unlike the azide, the coordinating COD of 7 was easily replaced by carbon monoxide[17]. Under the atmospheric pressure of CO, a stirring solution of 7 gave the desired car-bonyl substituted rhodium complex 9 quantitatively

(Scheme 4). IR spectrum of this complex showed two

car-bonyl stretching at 2084 and 2031 cm1, characteristics for rhodium dicarbonyl moiety. The coordination of the strong p-acid ligands toward metal center causes the down-field shift of protons on both pyridine and imidazole rings in the1H NMR spectrum. A broad signal between 6.20 and 5.20 ppm, with the integration of two protons, was assigned to be the benzylic ones, which is due to the rapid conformation flip of the chelating ring. By lowering the temperature, two sets of doublets was observed, which allowed us to determine the DG6¼= 54.3 kJ/mol for the process. The coordinated carbene ligand of 9 manifests a pair of doublet at 172.0 in 13C{1H} NMR spectrum with rhodium–carbon coupling of 44.9 Hz, which is upfield shift by ca. 2 ppm as compared to that of 7. Furthermore, X-ray single crystal diffraction was determined to confirm the structure.

ORTEP diagram of 9 is represented in Fig. 5, and selected bond distances and bond angles can be found in

Table 1. As expected, the geometry around the rhodium

center is square planar, with the chelating pyNC [bite angle 87.2(1)] and two carbonyl ligands. The chelating ring is adopted in a boat conformation, which allows the two methylene protons in diﬀerent environments. This is in agreement with the spectroscopic analysis. The bond lengths of Rh–C(carbene) [2.051(4) A˚ ] and Rh–C(carbonyl)

[1.828(5) and 1.919(5) A˚ ] lie in the normal range. The Rh–C(carbonyl) trans to the carbene moiety appears to be

N Ar' N N Ar' Rh(COD) N3 NaN₃/EtOH [(COD)RhCl]2 7 8 NaN₃/EtOH 6

Scheme 3. Activity of rhodium azido complexes.

Fig. 4. Molecular structure of rhodium azide complex 8 (30% probability ellipsoids). N Ar' N N C Ar' N Ar' NC_N _Ar' Rh(COD) Ph₃P BF4 N Rh N C Ar' N Ar' BF4 CO NaN3 PPh₃ 10 6 7 (COD)Rh N3 OC 8 9 CO P(OMe)₃ N Ar' NC_N _Ar' Rh (MeO)₃P BF₄ 11 P(OMe)₃ P(OMe)₃

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longer than that of cis by about 0.1 A˚ , as anticipated, due to the trans inﬂuence. Dihedral angles between rhodium coordination plane and mesityl rings are 62.58 and 80.45, showing that these two aromatic rings are bisected with the coordination plane. These two aryl rings along with ortho methyl groups make these two carbonyl ligands adopting into a packet, which causes the angle Rh(1)– C(29)–O(2) [171.2(4)] deviated from 180 for a relief of the steric interaction.

The chelation as well as the protection of bulky substit-uents of the carbene ligand (pyNC) around the metal cen-ter renders this carbonyl complex fairly stable. The complex does not show any decomposition in air for weeks. Even the treatment of some strong oxidizing agents such as H2O2, complex 9 stays intact as evidenced by its

spectro-scopic analysis.

2.3.3. Phosphine and phosphite

Treatment of complex 7 with molar equivalent amount of triphenylphosphine led to the dissociation of the pyridi-nyl nitrogen with the formation of a cationic phosphine-substituted rhodium carbene complex 10 (Scheme 4). The resulting complex 10 showed a sharp doublet with JRh–P=

153.5 Hz in the31P{1H} NMR spectrum and a set of dou-blet of doudou-blet at d 177.5 with JRh–C= 50.9 Hz, JP–C=

12.1 Hz for carbene-carbon in 13C{1H} NMR spectrum, indicating the coordination of phosphine to the metal cen-ter. Addition of excess triphenylphosphine did not proceed a further substitution on the metal center. This observation clearly illustrates that the coordination ability of triphenyl-phosphine, a monodentate, is stronger than that of the che-lating pyridinyl nitrogen, but weaker than that of a diaminocarbene donor. The steric bulkiness around metal center also inﬂuences the ligand substitution. For example, complex 7 does not proceed the reaction with tri-tert-butyl-phosphine in chloroform even under reﬂuxing conditions.

Unlike complex 7, this phosphine substituted rhodium complex 10 became air sensitive and was slowly oxidized to yield phosphine-oxide and the chelation complex 7. Pre-sumably, the de-complexation of pyrininyl nitrogen donor readily opens up the ‘‘packet’’, allowing that the ligands on the rhodium center are labile. Thus, the dissociation of phosphine-oxide provided the chelation of pyNC and yield the complex 7 again.

Treatment complex 7 with 3 equiv. of P(OCH3)3resulted

in the formation of tris(trimethylphosphite)rhodium com-plex 11. Apparently, pyridinyl-nitrogen and COD were all substituted by phosphite ligands, a p-acid donor. This new tris(phosphite)rhodium carbene complex showed two sets of signals in31P{1H} NMR spectrum: one of which showing doublet of doublet at 130.9 with JRh–P

= 222.2 Hz and JP–P= 70.0 Hz was assigned to the two

phosphites in trans relationship; the other one in triplet of doublet at 138.5 with JRh–P= 191.7 Hz, JP–P= 70.0 Hz

was due to the phosphite trans to the carbene ligand. Observation of m/z = 870.2280 on the HR-FAB mass spec-trum, consistent with the formula of C36H56N3O9P3103Rh,

clearly illustrated the existence of complex 11.

In contrast to monophosphine, both COD and pyNC ligands of complex 7 were completely substituted by bis-phosphine ligands such as dppe [1,2-bis(diphenylphosph-ino)-ethane] or dppp [1,3-bis(diphenylphosphino)propane]. Thus reaction of 7 with two equimolar amount of bisphos-phine gave [(bisphosbisphos-phine)2Rh]+ species (Scheme 5). The

resulting bisphosphine complexes was subsequently oxi-dized with molecular oxygen to form [Rh(bisphos-phine)2(O2)]+species[18,19]. N Ar' N N C Ar' BF4 14 N Ar' Rh (COD) C N N Ar' PPh 3 P(t-Bu) 3 Ar' = 2,4,6-trimethylphenyl 11 BF₄ (COD) Rh PPh₃ X DPPE or DPPP Rh bis(diphosphine) cation

Scheme 5. Replacement of carbene ligand by bisphosphine. Fig. 5. ORTEP diagram of cationic part of complex 9 (30% probability

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3. Summary

The synthetically easily accessible rhodium carbene complex 6 is a good precursor for further coordination study. Considering the results of this study, it is obvious that the pyridinyl-nitrogen donor is labile in the rhodium complexes particularly in the presence of other r-donors. With p-acceptor ligands, this bidentate shows its chela-tion eﬀect and steric hindrance on stabilizachela-tion of the complex itself. However, the diaminocarbene ligand can be easily replaced by a bisphosphine, suggesting a favor-able chelation eﬀect of phosphine toward rhodium(I) ion center.

4. Experimental 4.1. General

All reactions and manipulations were performed under a dry nitrogen atmosphere unless otherwise noted. Tetrahy-drofuran was distilled under nitrogen from sodium benzo-phenone ketyl. Dichloromethane was dried over CaH2and

distilled under nitrogen. Other solvents were degassed before use. Chemicals were purchased from commercial source and used without further puriﬁcation.

Nuclear magnetic resonance spectra were recorded in CDCl3 or acetone-d6 on either a Bruker AM-300 or

AVANCE 400 spectrometer. Chemical shifts are given in parts per million relative to Me4Si for 1H and 13C{1H}

NMR, and relative to 85% H3PO4for31P NMR. Infrared

spectra were measured on a Nicolet Magna-IR 550 spec-trometer (Series-II) as KBr pallets, unless otherwise noted. 4.2. Synthesis and characterization

4.2.1. 6-Mesityl-pyridine-2-carboxaldehyde (4)

To a solution of 6-bromopyridine-2-carboxaldehyde (1.00 g, 5.38 mmol), mesitylboronic acid (1.34 g, 8.17 mmol) and Pd(PPh3)4 (0.25 g, 0.22 mmol, 5 mol%) in

tol-uene (34 ml) and methanol (8.5 ml) under nitrogen was added an aqueous sodium carbonate solution (2 M, 17.5 ml). The resulting mixture was heated to reﬂux for 16 h. Upon cooling, the organic layer was collected and the water layer was extracted with ethyl acetate (50 mL ·2). All organic extracts were combined and dried with MgSO4. After the concentration, the residue was

chro-matographed on silica gel with elution of ethyl acetate/ hexane = 1/20 (Rf= 0.6) to give the desired product 4

as white solids (1.09 g, 90%): 1H NMR (400 MHz, CDCl3) d 10.09 (s, 1H), 7.92 (m, 1H), 7.47–7.43 (m, 2H), 6.92 (s, 2H), 2.32 (s, 3H), 2.01 (s, 6H). 13C{1H} NMR (100 MHz, CDCl3) d 193.7, 160.6, 152.6, 138.0, 137.2, 136.3, 135.5, 129.0, 128.4, 119.3, 21.2, 20.3. IR (KBr, cm1): 3072 (w), 2933 (s), 2853 (s), 2740 (w), 2687 (w), 1706 (vs), 1600 (s), 1454 (s). Anal. Calc. for C15H15NO: C, 79.97; H, 6.71; N, 6.22. Found: C, 80.08;

H, 6.88; N, 5.96%.

4.2.2. 1-(6-Mesityl-2-picolyl)-3-mesitylimidazolium bromide (3)

To a solution of 4 (1.09 g, 4.85 mmol) in methanol (10 ml) was added into the NaBH4(0.28 g, 7.27 mmol) in

methanol (10 ml) at 0C. The resulting solution was then heated to reﬂux for 1 h. Upon evaporation of MeOH, 2-hydroxymethyl-6-mesityl-pyridine was obtained as white solids by the addition of water (10 ml) to the residue. With-out further puriﬁcation, this alcohol was used for the fol-lowing transformation. PBr3 (0.7 ml, 7.45 mmol) was

added to a solution of 2-hydroxymethyl-6-mesityl-pyridine (0.65 g, 2.86 mmol) in CH2Cl2(13 ml) at 0C. The mixture

was stirred at room temperature overnight and then treated with water (10 mL). Upon neutralization, the reaction mix-ture was washed with saturated sodium bicarbonate aque-ous solution and the organic portion was separated. The organic layer was collected and dried with MgSO4. Upon

concentration, the desired bromide was collected and used for the following step. A mixture of 2-bromomethyl-6-mesitylpyridine and 1-mesitylimidazole (0.54 g, 2.90 mmol) in THF (20 ml) was then added. The resulting mixture was heated to reﬂux overnight. During the reaction, white sol-ids gradually precipitated, which was collected by ﬁltration (1.30 g, 95%):1H NMR (400 MHz, CDCl3) d 10.23 (s, 1H), 8.00 (s, 1H), 7.96 (d, 1H, J = 7.2 Hz), 7.81 (dd, 1H, J = 7.2 Hz, 7.2 Hz), 7.18 (d, 1H, J = 7.2 Hz), 7.03 (s, 1H), 6.94 (s, 2H), 6.89 (s, 2H), 6.19 (s, 2H), 2.30 (s, 6H), 1.94 (s, 6H), 1.89 (s, 6H). 13C{1H} NMR (100 MHz) d 159.6, 152.0, 140.8, 137.7, 137.5, 137.3, 136.7, 135.0, 133.9, 130.3, 129.4, 127.9, 124.5, 123.6, 122.2, 121.4, 53.8, 21.0, 20.1, 17.3. Anal. Calc. for C27H30N3Br: C, 68.06; H,

6.35; N, 8.82. Found: C, 68.13; H, 6.03; N, 8.88%. 4.2.3. Silver carbene complex (5)

To a solution of 6 (0.73 g, 1.53 mmol), silver oxide (0.18 g, 0.78 mmol) and sodium iodide (0.24 g, 1.60 mmol) in CH2Cl2 (20 ml) were stirred at room temperature for

48 h. Filtration of the reaction mixture through Celite gave a colorless solution, which was then concentrated. Upon the addition of hexane to the crude reaction mixture, com-plex 5 was precipitated and isolated as white solids (0.92 g, 95%). 1H NMR (400 MHz, CDCl3) d 7.74 (dd, 1H, J = 8.0 Hz, 8.0 Hz), 7.45 (d, 1H, J = 8.0 Hz), 7.36 (d, 1H, J = 1.6 Hz), 7.16 (d, 1H, J = 8.0 Hz), 6.91 (s, 2H), 6.88 (s, 2H), 6.84 (d, 1H, J = 1.6 Hz), 5.51 (s, 2H), 2.30 (s, 6H), 1.94 (s, 6H), 1.86 (s, 6H). 13C{1H} NMR (100 MHz) d 183.5(Ag@C), 159.4, 154.9, 138.5, 137.6, 137.2, 137.1, 135.3, 135.2, 134.6, 128.8, 128.1, 124.0, 122.1, 122.0, 121.2, 57.0, 21.2, 21.1, 20.3, 17.8. HR-FABMS for [M+]: Calc. 897.3774 (C54H58N6107Ag):

Found: 897.3765. Anal. Calc. for C54H58N6Ag2I2: C,

51.45; H, 4.64; N, 6.67. Found: C, 51.28; H, 4.44; N, 6.60%. 4.2.4. (C-pyNC)Rh(COD)Cl (6)

A mixture of silver complex 5 (630 mg, 0.98 mmol) and [RhCl(COD)]2 (242 mg, 0.49 mmol) in dichloromethane

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resulting solution was ﬁltrated through Celite followed by concentration and crystallization from CH2Cl2/hexane to

aﬀord yellow crystalline solids (635 mg, 99%): 1H NMR (400 MHz, CDCl3) d 7.79 (dd, 1H, J = 7.2 Hz, 7.2 Hz), 7.69 (d, 1H, J = 7.2 Hz), 7.17 (d, 1H, J = 7.2 Hz), 7.11 (d, 1H, J = 1.6 Hz), 7.08 (s, 1H), 6.91 (s, 2H), 6.88 (s, 1H), 6.70 (d, 1H, J = 1.6 Hz), 6.39 (d, 1H, J = 14.8 Hz), 5.92 (d, 1H, J = 14.8 Hz), 4.91–4.78 (m, 2H), 3.27 (m, 1H), 2.93 (m, 1H), 2.45 (s, 3H), 2.36 (s, 3H), 2.31 (s, 3H), 2.24–2.10 (m, 2H), 2.03–1.94 (m, 1H), 1.98 (s, 6H), 1.75 (s, 3H), 1.73–1.64 (m, 3H), 1.49–1.42 (m, 2H). 13 C{1H} NMR (100 MHz) d 182.0 (d, JRh–C= 51 Hz), 159.1, 155.8, 138.0, 137.0, 136.6, 135.7, 135.1, 133.9, 129.1, 127.9, 127.7, 123.5, 122.6, 121.4, 120.9, 97.0 (d, JRh–C= 6.9 Hz), 96.9 (d, JRh–C= 7.6 Hz), 68.8 (d, JRh–C = 14.5 Hz), 67.5 (d, JRh–C= 14.4 Hz), 56.8, 34.1, 31.8, 29.4, 28.3, 21.4, 20.6, 20.1, 18.0. HR-FAB for [MCl]+: Calc. 606.2355 (C35H41N3 103 Rh), Found: 606.2357. Anal. Calc. for C35H41N3ClRh: C, 65.47; H, 6.44; N, 6.54. Found: C, 65.21; H, 6.69; N, 6.28%. 4.2.5. (C,N-pyNC)Rh(COD)(BF4) (7)

A mixture of complex 6 (221.3 mg, 0.35 mmol) and silver tetraﬂuoroborate (70.0 mg, 0.36 mmol) in CH2Cl2 (30 ml)

was stirred under nitrogen at the ambient temperature for 1 h. The mixture was ﬁltrated through Celite and the ﬁltrate was collected and concentrated. Recrystallization from a solution of CH2Cl2and hexane provided the desired

prod-uct as yellow crystalline solids, which were suitable for X-ray single crystal diﬀraction analysis. (230.1 mg, 96%): 1H NMR (400 MHz, CDCl3) d 8.14 (dd, 1H, J = 7.6 Hz, 1.2 Hz), 7.94–7.91(m, 2H), 7.22 (d, 1H, J = 1.6 Hz), 7.03 (s, 1H), 6.93 (s, 1H), 6.90 (s, 1H), 6.85 (s, 1H), 6.60 (d, 1H, J = 1.6 Hz), 6.38 (d, 1H, J = 14.0 Hz), 6.17 (d, 1H, J = 14.0 Hz), 4.68–4.64 (m, 1H), 3.81–3.79 (m, 1H), 3.63 (m, 1H), 2.66–2.60 (m, 1H), 2.48–2.40 (m, 1H), 2.35 (s, 3H), 2.33 (s, 3H), 2.31 (s, 3H), 2.06–1.93 (m, 4H), 1.89 (s, 3H), 1.86 (s, 3H), 1.64 (s, 3H), 1.64 (s, 3H), 1.43–1.39 (m, 1H), 1.23–1.14 (m, 2H). 13C{1H} NMR (100 MHz) d 174.2 (d, JRh–C= 52.5 Hz), 161.3, 154.7, 139.2, 139.0, 137.0, 136.1, 135.4, 134.8, 134.5, 128.6, 128.5, 128.1, 127.8, 127.6, 124.3, 123.3, 122.9, 98.2 (d, JRh–C= 7.6 Hz), 94.9 (d, JRh–C= 6.8 Hz), 73.5 (d, JRh–C= 13.7 Hz), 71.8 (d, JRh–C= 12.2 Hz), 56.7, 35.4, 32.0, 29.2, 26.5, 23.4, 21.5,

21.4, 21.1, 18.6, 18.2. Anal. Calc. for C35H41N3BF4Rh: C,

60.62; H, 5.96; N, 6.06. Found: C, 60.41; H, 6.07; N, 5.95%. 4.2.6. (C-pyNC)Rh(COD)(N3) (8)

Complex 6 (63.5 mg, 0.10 mmol) and sodium azide (19.8 mg, 0.31 mmol) was dissolved in ethanol (10 ml) and water (5 ml). The resulting solution was heat to reﬂux for 6 h under nitrogen. Removal of ethanol, the residue was extracted with ethyl acetate (20 ml· 3). All organic portions were combined and dried over MgSO4. Recrystallization

from ethyl acetate and hexane gave the desired complex in yellow solids (50.3 mg, 79%):1H NMR (400 MHz, CDCl3) d 7.81 (dd, 1H, J = 7.6 Hz, 7.6 Hz), 7.58 (d, 1H, J = 7.6 Hz), 7.18 (d, 1H, J = 7.6 Hz), 7.16 (s, 1H), 7.12 (s, 1H), 6.91 (s, 2H), 6.89 (s, 1H), 6.75 (s, 1H), 6.37 (d, 1H, J = 15.2 Hz), 5.82 (d, 1H, J = 15.2 Hz), 4.52 (m, 2H), 3.28 (m, 1H), 2.82 (m, 1H), 2.46 (s, 3H), 2.37 (s, 3H), 2.32 (s, 3H), 2.12–2.04 (m, 3H), 1.99 (s, 6H), 1.76 (s, 3H), 1.70– 1.60 (m, 3H), 1.46–1.44 (m, 2H). 13C{1H} NMR (100 MHz) d 181.9 (d, JRh–C= 52.5 Hz), 159.3, 155.7, 138.1, 137.1, 136.9, 136.7, 135.6, 135.1, 133.8, 129.1, 128.0, 127.8, 123.6, 122.9, 121.7, 120.4, 95.4 (d, JRh–C= 7.6 Hz), 94.8 (d, JRh–C= 7.6 Hz), 70.2 (d, JRh–C= 12.9 Hz), 69.0 (d, JRh–C= 13.7 Hz), 56.1, 33.9, 31.7, 29.6, 28.6, 21.5, 20.6, 18.4, 18.1. IR (KBr, cm1): 2038 (s), 1235 (w). Anal. Calc. for C35H41N6Rh: C, 64.81; H, 6.37; N,

12.96. Found: C, 64.66; H, 6.73; N, 12.70%. 4.2.7. (C,N-pyNC)Rh(CO)2(BF4) (9)

To a solution of complex 7 (111.6 mg, 0.16 mmol) in CH2Cl2 (30 ml) was stirring under CO (1 atm) for 3 h at

r.t. After ﬁltrating through Celite, the solution was concen-trated and yielded yellow solids. Recrystallization from CH2Cl2 and hexane provided yellow solids (95.8 mg,

93%), which are suitable for single crystal X-ray diﬀraction analysis. 1H NMR (400 MHz, CDCl3) d 8.28 (d, 1H, J = 8.0 Hz), 8.11 (dd, 1H, J = 8.0 Hz, 8.0 Hz), 8.06 (d, 1H, J = 2.0 Hz), 7.41 (d, 1H, J = 8.0 Hz), 6.97 (s, 2H), 6.96 (s, 2H), 6.91 (d, 1H, J = 2.0 Hz), 6.20–5.20 (2H, br), 2.34 (s, 6H), 1.98 (s, 6H), 1.91 (s, 6H). 13C{1H} NMR (100 MHz) d 183.2 (d, JRh–C= 70.8 Hz), 181.6 (d, JRh–C= 54.8 Hz), 172.0 (JRh–C= 44.9 Hz), 163.3, 154.4, 141.4, 140.3, 140.2, 136.6, 135.3, 134.2, 129.2, 128.9, 128.5, 127.7, 125.7, 124.5, 123.6, 55.1, 31.0, 28.1, 21.3, 21.2, 18.0. IR (KBr, cm1): 2933 (w), 2866 (w), 2084 (s), 2031 (s), 1620 (m), 1461 (m), 1070 (s). HR-FABMS: Calc. 554.1315 (C29H29N3O2103Rh), [M+]), 526.1366 (C28H29N3O103Rh, [M+CO]); Found: 554.1305 (C29H29N3O2103Rh),

526.1370 (C28H29N3O103Rh). Anal. Calc. for C29H29N3O2

-BF4Rh: C, 54.32; H, 4.56; N, 6.55. Found: C, 54.54; H,

4.85; N, 6.29%.

4.2.8. [(C-pyNC)Rh(COD)(PPh3)]BF4(10)

Complex 7 (18.5 mg, 0.027 mmol) and triphenylphos-phine (7.0 mg, 0.027 mmol) dissolved in acetone-d6

(0.4 ml) was shaked with sonicator at room temperature for 10 min. NMR spectrum showed the complete conver-sion into the phosphine-substituted complex. 1H NMR (400 MHz, CDCl3) d 7.96 (dd, 1H, J = 7.6 Hz, 7.6 Hz), 7.62–7.56 (br, 5H), 7.52–7.44 (m, 8H), 7.41 (s, 1H), 7.40 (d, 1H, J = 7.6 Hz), 7.39–7.36 (m, 3H), 7.27 (d, 1H, J = 7.6 Hz), 7.02 (s, 1H), 7.00 (s, 1H), 6.89 (s, 2H), 6.49 (d, 1H, J = 15.6 Hz), 5.42 (m, 1H), 4.71 (d, 1H, J = 15.6 Hz), 4.51 (m, 1H), 4.04 (m, 1H), 3.91 (m, 1H), 2.37 (s, 3H), 2.29 (s, 3H), 2.00–1.72 (m, 14H), 1.78 (s, 3H), 1.62 (s, 3H).31P{1H} NMR (161.9 MHz) d 24.1 (d, JRh–P= 153.5 Hz). 13C{1H} NMR (100 MHz) d 177.5 (dd, JRh–C= 50.6 Hz, JP–C= 11.8 Hz), 160.0, 155.6, 139.5, 137.7, 137.1, 136.7, 135.9, 135.4, 134.2, 131.9 (d, JP–C= 9.9 Hz), 131.2, 129.7, 129.2, 129.1 (d, JP–C=

(8)

9.1 Hz), 128.2, 128.1, 127.6, 124.3 (d, JP–C= 7.6 Hz), 120.6,

97.2 (dd, JRh–C= 8.4 Hz, JP–C= 8.4 Hz), 94.2 (d, JRh–C=

10.7 Hz), 94.1 (d, JRh–C= 8.3 Hz), 91.6 (d, JRh–C=

1.6 Hz), 56.9, 33.2, 32.2 (d, JRh–C= 3.8 Hz), 29.2, 28.8,

21.3, 21.1, 20.5, 20.4, 18.0. HR-FABMS for [M+]: Calc. 868.3267 (C53H56N3P103Rh), Found: 868.3278.

4.2.9. (C,N-pyNC)Rh[P(OMe)3]3(BF4) (11)

Trimethylphosphite (5.7 ll, 0.048 mmol) was added into the CDCl3 solution of complex 7 (11.0 mg, 0.016 mmol)

under nitrogen and mixed with sonication at r.t. Monitor-ing the reaction by31P NMR, substitution was completed within 10 min to yield complex 11. 1H NMR (400 MHz, CDCl3) d 7.89 (dd, 1H, J = 7.6 Hz, 7.6 Hz, Py), 7.29 (d,

1H, J = 7.6 Hz, Py), 7.23 (s, 1H, Im), 7.21 (d, 1H, J = 7.6 Hz, Py), 6.93 (s, 3H), 6.90 (s, 2H), 3.78–3.67 (m, 2H), 3.51–3.47 (m, 27H, OMe), 2.30 (s, 3H, Me), 2.27 (s, 3H, Me), 2.06 (s, 6H, Me), 2.00 (s, 6H, Me). 13C{1H} NMR (100 MHz) d 181.9 (ddt, JRh–C= 139.5 Hz, JP–C= 43.8 Hz, 18.2 Hz), 159.2, 154.4, 138.5, 137.1, 136.9, 136.6, 135.4, 134.8, 134.6, 128.4, 127.9, 124.1, 124.0, 123.6, 120.8, 120.7, 120.0, 56.9 (CH2), 52.1, 51.8, 51.7, 21.3, 21.1, 20.4, 18.2. 31P{1H} NMR (121.4 MHz) d 138.5 (dt, JRh–P= 191.7 Hz, JP–P= 70.0 Hz, trans-P(OMe)3), 130.9 (dd, JRh–P= 222.2 Hz, JP–P= 70.0 Hz, cis-P(OMe)3).

HR-FABMS for [M+]: Calc. 870.2284 (C36H56N3O9

-P3103Rh), Found: 870.2280.

4.2.10. [(PP)2Rh(O2)]BF4

Complex 7 (15.0 mg, 0.021 mmol) and diphosphine (17.8 mg of dppp or 17.2 mg of dppe, 0.043 mmol) were dissolved in CDCl3 under nitrogen with sonication. The

resulting mixture was monitored by 31P NMR spectrum. After the completeness of the replacement, the mixture was exposed to air for 24 h. The obtained complex was puriﬁed by extraction and concentration. [(dppp)2RhBF4]: 1 H NMR (400 MHz, CDCl3) d 7.21–7.03 (br, 40H), 2.23– 2.12 (br, 8H, CH2), 1.78 (br, 4H, CH2). 31P{1H} NMR d 8.4 (d, JRh–P= 130.8 Hz); [(dppp)2Rh(O2)BF4]: 1H NMR d 7.73 (br, 6H), 7.38–7.29 (m, 12H), 7.23–7.28 (br, 6H), 7.14–7.10 (m, 4H), 6.98 (br, 6H), 6.88–6.83 (m, 6H), 2.69–2.65 (m, 4H), 2.44–2.29 (br, 8H). 31P{1H} NMR d 15.9 (dt, JRh–P= 121.5 Hz, JP–P= 30.4 Hz), 12.2 (dt, JRh–P= 84.9 Hz, JP–P= 30.4 Hz); [(dppe)2RhBF4]: 1H NMR (400 MHz, CDCl3) d .36–7.28 (m, 10H), 7.18– 7.13 (m, 30H), 2.08–2.03 (br, 8 H, CH2). 31P NMR d 58.2 (d, JRh–P= 132.7 Hz); [(dppe)2Rh(O2)BF4]: 1H NMR (CDCl3) d 7.61 (m, 10H), 7.43–7.30 (m, 20H), 7.16–7.14 (m, 10H), 2.49–2.30 (m, 8H, CH2). 31 P{1H} NMR (CDCl3, 161.9MHz): d 51.8 (dt, JRh–P= 125.8 Hz, JP–P= 8.0Hz), 44.5 (dt, JRh–P= 94.3Hz, JP–P= 8.0

Hz). These spectral data were consistent with the litera-ture reported data [19].

4.3. X-ray crystallographic analysis

Crystals suitable for X-ray determination were obtained for 5–9 by recrystallization at room temperature. Cell parameters were determined either by a Nonius Kappa CCD diﬀractometer. Crystal data of these complexes are listed inTable 2. All OTEP plots are drawn with 30% prob-ability ellipsoids and partial labeling for clear view inFigs. 1–5. Other crystallographic data are deposited as support-ing information.

Table 2

Crystallographic data for 5–9

Complex 5 6 7 8 9

Formula C54H58AgIN6 C35H41ClN3Rh Æ 0.5 CH2Cl2 C35H41BF4N3Rh C35H41N6Rh C30H29BF4N3O2Rh Æ CH2Cl2

Fw 1025.83 684.53 693.43 648.65 726.20

Crystal system Monoclinic Triclinic Monoclinic Monoclinic Monoclinic

Space group P21/c P 1 P21/c P21/n P21/n a (A˚ ) 11.93060(10) 9.9510(1) 11.3879(2) 19.1836(2) 7.6849(1) b (A˚ ) 26.0899(3) 11.1440(2) 17.4662(4) 9.7555(1) 20.0418(3) c (A˚ ) 17.1421(2) 16.9640(2) 17.7733(3) 19.6249(2) 21.0343(3) a() 90 105.197(1) 90 90 90 b() 108.5000(7) 90.516(1) 108.583(1) 118.9360(7) 92.31(1) c() 90 113.683(1) 90 90 90 V (A˚3_{); Z} _{5060.05(9); 4} _{1648.56(4); 2} _{3350.8(1); 4} _{3214.21(6); 4} _{3237.05(8); 4} dcalc.(Mg/m 3 ) 1.347 1.379 1.375 1.340 1.490 F(0 0 0) 2096 710 1432 1352 1472 Crystal size (mm3) 0.15· 0.12 · 0.10 0.25· 0.20 · 0.15 0.35· 0.25 · 0.15 0.25· 0.20 · 0.15 0.25· 0.20 · 0.15 Reﬂections collected 29 659 13 174 17 338 23 363 18 682

Independent reﬂections [Rint] 11 504 [0.0433] 7470 [0.0170] 5904 [0.0399] 7346 [0.0346] 5690 [0.0328]

hRange () 1.6–27.5 2.10–27.46 1.68–25.00 2.07–27.47 2.03–25.00

Reﬁned method Full-matrix least-squares on F2 Goodness-of-ﬁt on F2 _1.040 _0.996 _0.987 _1.017 _1.066 R indices [I > 2r(I)] R1= 0.0570, wR2= 0.1366 R1= 0.0338, wR2= 0.0877 R1= 0.0442, wR2= 0.1267 R1= 0.0386, wR2= 0.0944 R1= 0.0468, wR2= 0.1288

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Acknowledgement

We thank the National Science Council, Taiwan, ROC for the ﬁnancial support (NSC94-2113-M-002-035). Appendix A. Supplementary material

Crystallographic data (excluding structure factors) for the structure reported in this work have been deposited with the Cambridge Crystallographic Data Center: CCDC nos. 295075 (complex 5), 295076 (complex 8), 295077 (com-plex 7), 295078 (com(com-plex 6) and 295079 (com(com-plex 9). Cop-ies of this information can be obtained free of charge and by application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, fax: +44 1223 336 033, e-mail: deposit@ ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk. Sup-plementary data associated with this article can be found, in the online version, at doi:10.1016/j.jorganchem.2006. 06.004.

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