Insertion reactions of phenyl isocyanate into hafnium nitrogen bonds: synthesis and reactivity of hafnium complexes bearing substituted pyrrolyl ligands

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Insertion reactions of phenyl isocyanate into hafnium nitrogen

bonds: synthesis and reactivity of hafnium complexes

bearing substituted pyrrolyl ligands

Kun-Chun Hsieh

a

, Wen-Yi Lee

a

, Chun-Liang Lai

a

, Ching-Han Hu

a

, Hon Man Lee

a

,

Jui-Hsien Huang

a,*

, Shie-Ming Peng

b

, Gene-Hsing Lee

b

a

Department of Chemistry, National Changhua University of Education, Changhua 500, Taiwan

b

Department of Chemistry, National Taiwan University, Taipei 100, Taiwan Received 26 March 2004; accepted 27 July 2004

Available online 27 August 2004

Abstract

A bis(diethylamido)hafnium compound [C4H3N(CH2NMe2)-2]2Hf(NEt2)2 (1) has been prepared in 79% yield by reacting

Hf(NEt2)4with 2 equiv. of [C4H3NH(CH2NMe2)-2] in heptane via deamination. Reacting compound 1 with 2 equiv. of phenyl

iso-cyanate at room temperature in diethyl ether results in the PhNCO being inserted seletively into hafnium–NEt2bonds to generate

[C4H3N(CH2NMe2)-2]2Hf[PhNC(NEt2)O]2(2) in 56% yield. Similarly, while reacting 1 with 2 equiv. of phenyl isocyanate for a week

in toluene produces a mixture of 2 and [C4H3N(CH2NMe2)-2]Hf[PhNC(NEt2)O]3(3). For comparison, reacting Hf(NEt2)4with 4

equiv. of PhNCO in a toluene solution at room temperature results in the PhNCO inserted into Hf–N bonds, and forms a tetrakis-ureato hafnium compound Hf[PhNC(NEt2)O]4(4) in 88% yield. A theoretical calculation found that the unpaired electrons of the

ureato fragments of 2 are resonance delocalized between the C–O, C–NPh, and C–NEt2 bonds, which are all partially doubly

bonded.

Keywords: Phenyl isocyanate; Insertion hafnium; Pyrrolyl

1. Introduction

Organic isocyanates are useful compounds in organic synthesis because they are easily accessible and highly active toward unsaturated substrates [1]. In addition, isocyanate compounds are widely used in

polymeriza-tion chemistry for producing polyurethane [2]. Some

of the organic reactions of isocyanates are catalyzed

by transition metal complexes [3–7] and the reactions

of organic isocyanates with transition metals have been studied extensively. An excellent review by Braunstein

and Nobel [8] described the transition-metal-mediated

reactions of organic isocyanates, which covered a broad range of metal complexes. Insertion reactions of isocya-nates into metal carbon or metal nitrogen bonds have been known [9–12]; however, the insertion reactions of isocyanates into early transition metal–nitrogen bonds

still remain undeveloped [13–19]. Examples showed by

Lappert and coworkers [20] were those M(NMe2)4

(M = Ti, Zr, Hf) react exothermically with excess of

phenyl isocyanates to give M[NPhC(O)NMe2]4.

How-ever, no crystal structures were presented.

To better understand the reactivity of isocyanates toward early transition metal nitrogen bonds, here we report the synthesis and characterization of hafnium amide complexes and their reactivity toward isocyanates.

* _{Corresponding author. Tel: +886 4 723 2105x3531; fax: +886 4}

721 1190.

E-mail address:juihuang@cc.ncue.edu.tw(J.-H. Huang).

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2. Results and discussion

2.1. Synthesis and characterization

A bis(diethylamido)hafnium compound [C4H3N(CH2

NMe2)-2]2Hf(NEt2)2(1) has been prepared in 79% yield

by a deamination reaction between Hf(NEt2)4 and 2

equiv. of [C4H3NH(CH2NMe2)-2] in heptane (Scheme

1). Compound 1 is highly air- and moisture sensitive, which readily decomposes upon exposure to the atmos-phere. The1H and13C NMR spectra of 1 exhibit a sym-metrical geometry with only one set of signals for the substituted pyrrolyl and diethylamido ligands being observed.

Reactions of compound 1 with CO2and CS2do not

result in isolable insertion products, but rather aﬀord the regeneration of substituted pyrrolyl ligands and un-identiﬁed products. In contrast, reaction of 1 with 2 equiv. of phenyl isocyanate at room temperature in diethyl ether for 30 min results in the PhNCO being

in-serted selectively into Hf–NEt2 bonds to generate

[C4H3N(CH2NMe2)-2]2Hf[PhNC(NEt2)O]2 (2) in 56%

yield. The13C NMR spectrum of 2 revealed a resonance at d 165.9, which is assignable to the quaternary carbons

of ureato PhNC(NEt2)O fragments. The

1

H NMR spec-trum of 2 obtained from a 300 MHz NMR spectrometer contains sharp resonances at d 6.59 and 6.45 attributable to the pyrrolyl fragments of the bidentate ligands. How-ever, the dimethylamino fragments of the bidentate lig-ands (d 2.18) as well as the diethylamino fragments (d 2.78 and 0.73) exhibit broad signals. The signal-broad-ening can probably be attributed to the ﬂuxionality of

the ureato PhNC(NEt2)O fragments of 2, which bind

to its metal center in various modes, as shown in Scheme 2. The broad signals can be resolved in higher ﬁeld NMR spectrometer. When a 600 MHz NMR spec-trometer was used, the1H NMR spectra of 2 exhibit two peaks for the dimethylamino groups and multiple reso-nances for the diethyl amino fragments. A comparison

of the 1H NMR spectra of 2 obtained from 300 and

600 MHz NMR spectrometers was shown inFig. 1.

Prolong stirring of 1 with 2 equiv. of PhNCO in tol-uene at room temperature for 6 days, a mixture of com-pounds 2 and [C4H3N(CH2NMe2)-2]Hf[PhNC(NEt2)

O]3(3) can be obtained according to the1H NMR

spec-tra. Pure compound 3 can be obtained in 14% yield after removing volatiles and repeating recrystallization of the

mixture from a diethyl ether solution. The 13C NMR

spectrum of 3 revealed two resonances at d 166.2 and 167.0, which are assignable to the quaternary carbons

of ureato PhNC(NEt2)O fragments. Again, the

dimeth-ylamino fragments of the bidentate ligands (d 2.67) as well as the diethylamino fragments (d 2.27–2.73 and 0.73) exhibit broad signals due to the exchanging of

bonding modes as shown in Scheme 2. No reaction

was observed when monitoring a C6D6 solution of 2

for more than 80 h. Therefore, the formation of 3 was proposed as the results of ligand redistribution, which only occurs when excess of PhNCO is present. Indeed, when small amount of PhNCO was added to the a

solu-tion of compound 2 in C6D6, 3 was formed together

with several un-identiﬁed compounds within 12 h at

50 °C, according to the 1H NMR spectra. However,

the real mechanism for the ligand redistribution is still unclear. Attempts to increase the yield of compound 3 by reacting 1 with 3 equiv. of PhNCO in toluene result

Hf(NEt2)4 N H NMe2 2 N NMe2 N NMe2 Hf NEt2 NEt2 N NMe2 N NMe2 Hf 2 O N Ph NEt2 O N Ph NEt2 1 2 PhNCO N NMe2 Hf O N Ph NEt2 O N Ph NEt2 O N Ph Et2N 3 2 PhNCO diethyl ether toluene 2 + 6 days Scheme 1.

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in a mixture of 2, 3, 4, and several un-identiﬁed prod-ucts. Therefore, we conclude that when 2 equiv. of PhNCO was added in a solution of 1, it can only insert selectively into the Hf–amide bonds and only com-pounds 2 and 3 can be isolated. However, addition of PhNCO into hafnium–pyrrolyl bond may occur when excess of PhNCO was presented in the reaction solution (i.e., > 2 equiv.), according to 1H NMR spectra [21]. The reaction became complicate and several un-identi-ﬁed products besides 2 and 3 were found. All the at-tempts to isolate new compounds are not successful.

For comparison, reacting Hf(NEt2)4with 4 equiv. of

PhNCO in a toluene solution at room temperature re-sults in the PhNCO inserted into Hf–N bonds forming a tetrakis–ureato hafnium compound Hf[PhNC(NE-t2)O]4(4) in 88% yield (Scheme 3). A similar compound,

Hf[PhNC(NMe2)O]4, has been synthesized by Lappert

and coworkers[20]. The1H NMR spectrum of 4 exhibits only one set of quartet and triplet at d 2.89 and 0.71 for the ethyl protons of diethylamino groups, indicating

that the four ureato PhNC(NEt2)O groups are

equiva-lent in solution at room temperature. The 13C NMR

spectrum of 4 exhibited a singlet at d 166.6 for the qua-ternary carbon of ureato PhNC(NEt2)O, which is

simi-lar to that of 2.

2.2. Molecular structures of compounds 1, 2, 3 and 4 Crystals of 1 suitable for crystallographic studies

were obtained from a toluene solution at 20 °C.

Molecular structure of 1 and selected bond distances and angles are given inFig. 2andTable 1, respectively. The geometry of 1 is best described as a distorted octa-hedral with bond angles of the three axes N(1)–Hf(1)–

N(6), N(4)–Hf(1)–N(5), and N(2)–Hf(1)–N(3) of

153.54(9)°, 162.45(8)°, and 165.08(8)°, respectively. The two substituted pyrrolyl ligands bond to the haf-nium center with acute angles of 70.82(9)° and 71.22(8)°. The two diethylamido ligands bind to the Le-wis acidic hafnium atom in an asymmetrical manner and result in a short bond distance of Hf(1)–C(19) (2.845(3)

A˚ ) with small bond angle of Hf(1)–N(6)–C(19)

(106.20(19)°). However, the two diethylamido ligands

Hf(NEt2)4 _Hf 4 O N Ph NEt2 O N Ph NEt2 4 PhNCO _O N Ph Et2N O N Ph Et2N Scheme 3.

Fig. 2. The molecular structure of 1. Thermal ellipsoids were drawn at 50% probability level.

Fig. 1. The1_{H NMR spectra for compound 2 ranged from d 0–3,}

asterisk (*) represent un-identiﬁed products (a) 300 MHz NMR spectrometer (b) 600 MHz spectrometer. Hf O C N Ph NEt2 Hf O C N Ph NEt2 Hf O C N Ph NEt2 Scheme 2.

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become equivalent in solution due to their low rotation energy barriers.

Crystals of 2 were obtained from a diethyl ether

solu-tion at 20 °C. The molecular structure and selected

bond distances and angles of 2 are shown in Fig. 3

and Table 1, respectively. Compound 2 can be viewed as an eight coordinated hafnium compound with the two ureato ligands are bonded to hafnium through nitrogen and oxygen atoms. Compound 2 possesses two planar ureato metallacycles, which contain obtuse N–C–O angles of 112.5(9)° and 111.8(9)°, as well as acute N–Hf–O angles of 59.1(3)° and 58.9(3)°. The two substituted pyrrolyl ligands bond to the hafnium center with acute angles of 67.1(3)° and 66.6(3)°, smaller

than those of compound 1, presumably due to the larger ureato ligands compressing the bond angles of the che-lated substituted pyrrolyl ligands. The N–C (ranged from 1.327(12) to 1.338(13) A˚ ) and C–O (1.287(11) to 1.312(11) A˚ ) bond distances of ureato fragments are both in the range of partially double bond, indicating that the p electrons of the ureato fragments are equally delocalized in the NC(N)O core.

Crystals of 3 suitable for crystallographic studies were obtained after repeating recrystallization of a mix-ture of compounds 2 and 3 diethyl ether solution at 20 °C. The molecular structure and selected bond dis-tances and angles of 3 are shown inFig. 4andTable 1, respectively. A disorder occurred at one of the methyl

Table 1

Selected bond distances and angles for compounds 1, 2, 3 and 4 1 Hf(1)–N(1) 2.207(3) Hf(1)–N(2) 2.495(2) Hf(1)–N(3) 2.174(2) Hf(1)–N(4) 2.635(2) Hf(1)–N(5) 2.023(2) Hf(1)–N(6) 2.046(2) N(1)–Hf(1)–N(2) 70.82(9) N(3)–Hf(1)–N(4) 71.22(8) N(1)–Hf(1)–N(6) 153.54(9) N(2)–Hf(1)–N(3) 165.08(8) N(4)–Hf(1)–N(5) 162.45(8) 2 Hf(1)–N(1) 2.202(8) Hf(1)–N(2) 2.563(9) Hf(1)–N(3) 2.229(8) Hf(1)–N(5) 2.207(8) Hf(1)–N(6) 2.552(11) Hf(1)–N(7) 2.253(9) Hf(1)–O(1) 2.188(7) Hf(1)–O(2) 2.189(7) Hf(1)–C(8) 2.648(10) Hf(1)–C(26) 2.668(11) N(3)–C(8) 1.334(12) C(8)–O(1) 1.287(11) C(8)–N(4) 1.338(12) N(7)–C(26) 1.327(12) C(26)–O(2) 1.312(11) C(26)–N(8) 1.336(13) N(1)–Hf(1)–N(2) 67.1(3) N(5)–Hf(1)–N(6) 66.6(3) O(1)–Hf(1)–N(3) 59.1(3) O(2)–Hf(1)–N(7) 58.9(3) N(2)–Hf(1)–C(26) 161.7(3) N(6)–Hf(1)–C(8) 165.1(3) N(3)–C(8)–O(1) 112.5(9) N(7)–C(26)–O(2) 111.8(9) 3

Hf(1)–O(3) 2.181(6) Hf(1)–O(2) 2.189(5) Hf(1)–O(1) 2.191(6)

Hf(1)–N(7) 2.206(6) Hf(1)–N(1) 2.250(6) Hf(1)–N(5) 2.251(6) Hf(1)–N(3) 2.260(6) Hf(1)–N(8) 2.468(6) Hf(1)–C(7) 2.636(8) Hf(1)–C(18) 2.652(8) Hf(1)–C(29) 2.656(9) N(1)–C(7) 1.304(10) O(1)–C(7) 1.286(9) O(2)–C(18) 1.295(9) N(3)–C(18) 1.38(11) O(3)–C(29) 1.316(12) N(5)–C(29) 1.313(11) N(7)–Hf(1)–N(8) 88.1(2) O(1)–Hf(1)–N(1) 58.5(2) O(2)–Hf(1)–N(3) 58.9(2) O(3)–Hf(1)–N(5) 59.1(2) 4 Hf(1)–N(1) 2.264(3) Hf(1)–N(3) 2.251(3) Hf(1)–N(5) 2.251(3) Hf(1)–N(7) 2.252(6) Hf(1)–O(1) 2.208(4) Hf(1)–O(2) 2.185(3) Hf(1)–O(3) 2.184(3) Hf(1)–O(4) 2.189(3) Hf(1)–C(1) 2.658(4) Hf(1)–C(12) 2.647(4) Hf(1)–C(23) 2.653(4) Hf(1)–C(34) 2.655(4) O(1)–C(1) 1.275(6) C(1)–N(2) 1.361(5) C(1)–N(1) 1.356(6) O(2)–C(12) 1.289(4) C(12)–N(4) 1.349(5) C(12)–N(3) 1.355(5) O(3)–C(23) 1.294(4) C(23)–N(6) 1.347(5) C(23)–N(5) 1.329(5) O(4)–C(34) 1.294(4) C(34)–N(8) 1.346(5) C(34)–N(7) 1.340(7) O(1)–Hf(1)–N(1) 58.96(15) O(2)–Hf(1)–N(3) 59.55(10) O(3)–Hf(1)–N(5) 59.04(10) O(4)–Hf(1)–N(7) 59.23(16) O(1)–C(1)–N(1) 113.6(4) O(2)–C(12)–N(3) 112.9(3) O(3)–C(23)–N(5) 112.8(3) O(4)–C(34)–N(7) 112.9(4)

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carbon which was separated into C(33) and C(33)0 _with

the occupancy ratio of 60/40. The bond distances and angles of 3 were similar to those of 2.

Even though Hf[PhNC(NMe2)O]4, analogous to

compound 4, has been synthesized[20], no crystal struc-ture of that has been obtained. Crystals of 4 suitable for crystallographic studies were obtained from a toluene solution at20°C. The molecular structure and selected bond distances and angles of 4 are shown inFig. 5and Table 1, respectively. Compound 4 can also be viewed as

an eight coordinate MX8 geometry [22] where ureato

fragments bond to the hafnium atom through nitrogen and oxygen atoms. A simpliﬁed geometry of 4 is shown inFig. 6where the eight coordinated atoms are located

on two perpendicular rectangles or in an idealized cube. The four ureato fragments coordinate to the hafnium atom forming four planar metallacycles. The bond dis-tances and angles of 4 around the ureato metallacycles are similar to that of 2, indicating that the p electrons of ureato fragments are evenly distributed.

2.3. Theoretical calculation

All calculations were performed using the hybrid B3LYP density functional theory [23,24]. For the basis sets we chose 6-31 G* for H, C, N, O, and LANL2DZ eﬀective core potential plus basis functions for hafnium [25,26]. The reaction of 1 with PhNCO, which yields 2,

was calculated as an exothermic reaction with 65.7

kcal/mol for the heat of emission. The calculated bond distances and angles of 1 and 2 are close to the experi-mental data (seesupporting information). As suggested in Scheme 2, the unpaired electrons of the ureato frag-ments of 2 are resonance delocalized between the C–O, C–NPh, and C–NEt2bonds, which are all partially

dou-bly bonded.

Fig. 4. The molecular structure of 3. Thermal ellipsoids were drawn at 30% probability level. C(33) and C(33)0 _{are disorder sites with}

occupancy ration of 60/40.

Fig. 5. The molecular structure of 4. Thermal ellipsoids were drawn at 30% probability level. N O O N Hf N N O O 0 0 0 0 0 0 0 Hf 0 N N N N O O O O (a) (b)

Fig. 6. Hf(g3-NCO)4 core inscribed within (a) two perpendicular

rectangles and (b) an idealized cube showing the eight coordinate HfN4O4unit.

Fig. 3. The molecular structure of 2. Thermal ellipsoids were drawn at 30% probability level.

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3. Experimental 3.1. General procedure

All reactions were performed under a dry nitrogen atmosphere using standard Schlenk techniques or in a glove box. Toluene, diethyl ether, and heptane were dried by reﬂuxing over sodium benzophenone ketyl. CH2Cl2was dried over P2O5. All solvents were distilled

and stored in solvent reservoirs which contained 4 A˚ molecular sieves and were purged with nitrogen. CDCl3

was degassed by freeze-and-thaw method and dried over 4 A˚ molecular sieves.1H and13C NMR spectra were re-corded on a Bruker AC 200 or an Avance 300 NMR spectrometer at room temperature if not stated other-wise. Chemical shifts for 1H and 13C spectra were re-corded in ppm relative to the residual protons and13C of CDCl3(d 7.24, 77.0) and C6D6 (d 7.16, 128.0).

Ele-mental analyses were performed on a Heraeus CHN-OS Rapid Elemental Analyzer at the Instrument Center, NCHU. (2-dimethylaminomethyl)pyrrole was synthe-sized according to published literature [27,28]. HfCl4

was purchased from Aldrich Co. and used as received. 3.2. [C4H3N(CH2NMe2)-2]2Hf(NEt2)2(1)

To a 100 mL Schlenk ﬂask charged with 20 mL hep-tane and Hf(NEt2)4(3.0 g, 6.42 mmol) was added

drop-wise with a C4H4N(CH2NMe2) (1.59 g, 12.8 mmol)/

heptane (20 mL) solution at room temperature with stir-ring for 12 h. Volatiles were removed under vacuum and the resulting solids were recrystallized from a toluene solution to generate 2.89 g of white solids in 79% yield.

1 H NMR (C6D6): 7.18 (m, 2H, pyrrolyl CH), 6.56 (m, 2H, pyrrolyl CH), 6.32 (m, 2H, pyrrolyl CH), 3.48 (m, 12H, NCH2CH3 and CH2NMe2), 2.02 (s, 12H, CH2NMe2), 0.84 (t, 12H, NCH2CH3). 13C NMR (C6D6): 136.0 (s, pyrrolyl Cipso), 128.5 (d, JCH= 178 Hz, pyrrolyl CH), 109.4 (d, JCH= 165 Hz, pyrrolyl CH), 104.9 (d, JCH= 164 Hz, pyrrolyl CH), 63.0 (t, JCH= 137 Hz, CH2NMe2), 48.4 (q, JCH= 136 Hz, NMe2), 40.8 (t, JCH= 131 Hz, NCH2CH3), 13.0 (q,

JCH= 125 Hz, NCH2CH3). Anal. Calc. for

C22H42N6Hf: C, 46.43; H, 7.44; N, 14.77. Found: C,

45.60; H, 7.79; N, 15.23%.

3.3. [C4H3N(CH2NMe2)-2]2Hf[PhNC(NEt2)O]2(2)

To a 50 mL Schlenk ﬂask charged with 20 mL diethyl ether and 1 (2.0 g, 3.5 mmol) was added PhNCO (0.84 g, 7.1 mmol) via syringe at room temperature. The solu-tion color changed from pale yellow to dark red. Vola-tiles were removed under vacuum after 30 min stirring and the resulting solids were recrystallized from a diethyl ether solution to generate 1.59 g of white solids

in 56% yield. 1H NMR (C6D6): 7.67 (m, 2H, phenyl

CH), 7.27–6.95 (m, 10H, phenyl and pyrrolyl CH), 6.59 (m, 2H, pyrrolyl CH), 6.45 (m, 2H, pyrrolyl CH),

4.09 (d, JHH= 13.2 Hz, CHaHbNMe2), 3.14 (d,

JHH= 13.2 Hz, CHaHbNMe2), 2.78 (br, 8H, NCH2CH3),

2.18 (br, 12H, CH2NMe2), 0.79 (br, 6H, NCH2CH3),

0.60 (br, 6H, NCH2CH3). 13C NMR (C6D6): 165.9 (s,

NCO), 146.4 (s, phenyl Cipso), 136.3 (s, pyrrolyl Cipso),

129.9 (d, JCH= 181 Hz, pyrrolyl CH), 128.2 (d, JCH= 158 Hz, phenyl CH), 127.9, 122.9 (d, JCH= 160 Hz, phenyl CH), 107.0 (d, JCH= 163 Hz, pyrrolyl CH), 104.9 (d, JCH= 156 Hz, pyrrolyl CH), 61.2 (t, JCH= 134 Hz, CH2NMe2), 49.5 (q, JCH= 137 Hz, NMe2), 41.2 (t, JCH= 137 Hz, NCH2CH3), 13.2 (q,

JCH= 126 Hz, NCH2CH3). Anal. Calc. for

C36H52N8O2Hf: C, 53.56; H, 6.49; N, 13.88. Found: C,

52.73; H, 5.93; N, 13.99%.

3.4. [C4H3N(CH2NMe2)-2]Hf[PhNC(NEt2)O]3(3)

Similar procedure as for 2 has been used here. 1 (2.0 g, 3.5 mmol) and PhNCO (0.84 g, 7.1 mmol) were used and stirred for 6 days. Repeating recrystallization of resulting mixture from a diethyl ether solution yields 0.40 g of 3 in 14% yield. Small amount of 2 was found in the ﬁnal product.1H NMR (C6D6): 7.58 (m, 1H,

phe-nyl CH), 6.90–7.38 (br, 15H, phephe-nyl + pyrrolyl CH), 6.67 (m, 1H, pyrrolyl CH), 6.54 (m, 1H, pyrrolyl CH),

4.01 (m, 2H, CH2NMe2), 2.65–2.73 (br, 15H, N

CH2Me+NMe), 2.27 (br, 3H, NMe), 0.73 (br, 18H,

NCH2Me). 13C NMR (C6D6): 167.0 (s, NCO), 166.2

(s, NCO), 146.7 (s, br, phenyl, Cipso), 135.6 (s, pyrrolyl,

Cipso), 128.8 (d, JCH = 183 Hz, pyrrolyl CH), 128.3 (d,

JCH= 159 Hz, phenyl CH), 124.7 (d, JCH= 156 Hz,

phe-nyl CH,), 124.3 (d, JCH= 156 Hz, phenyl CH), 122.2 (d,

JCH= 162 Hz, phenyl CH), 106.4 (d, JCH= 174 Hz,

pyr-rolyl CH,), 103.0 (d, JCH= 163 Hz, pyrrolyl CH), 62.5

and 62.6 (two t, JCH= 139 Hz, CH2NMe2), 48.6 (q,

JCH= 140 Hz, NMe), 41.4 (t, JCH= 134 Hz, NCH2Me),

37.2 (q, JCH= 138 Hz, NMe), 13.4 (q, JCH= 128 Hz,

NCH2Me). No elemental analysis was performed due

to small amount of compound 2 was presented.

3.5. Hf[PhNC(NEt2)O]4(4)

To a 50 mL Schlenk ﬂask charged with 20 mL toluene

and Hf(NEt2)4 (1.0 g, 2.14 mmol) was added PhNCO

(1.02 g, 8.56 mmol) via syringe at room temperature. The color remained pale yellow after 1 h of stirring. Vol-atiles were removed under vacuum and the resulting sol-ids were recrystallized from a toluene solution at20 °C to generate 1.78 g of white solids in 88% yield.1H NMR (C6D6): 7.35–6.95 (m, 20H, phenyl CH), 2.89 (q, 16H,

NCH2CH3), 0.71 (t, 24H, NCH2CH3). 13C NMR

(C6D6): 166.6 (s, NCO), 147.9 (s, phenyl Cipso), 128.2

(d, JCH= 156 Hz, phenyl CH), 124.5 (d, JCH= 159

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41.4 (t, JCH= 137 Hz, NCH2CH3), 13.4 (q, JCH= 126

Hz, NCH2CH3). Anal. Calc. for C44H60N8O4Hf: C,

56.01; H, 6.41; N, 11.88. Found: C, 56.03; H, 6.07; N, 12.01.

4. X-ray structure determination of compounds 1, 2, 3 and 4 The crystals 1, 2, and 4 were mounted in glass ﬁ-bers under nitrogen and transferred to a goniostat. Data were collected on a Bruker SMART CCD dif-fractometer with graphite-monochromated Mo Ka

radiation with the radiation wavelength of

0.71073 A˚ . Data for crystal 3 were collected on a

Nonius KappaCCD diﬀractometer. A SADABS

absorption correction was made. All reﬁnements were carried out by full-matrix least squares using aniso-tropic displacement parameters for all non-hydrogen atoms. All the hydrogen atoms are calculated. The

crystal data are summarized in Table 2.

Acknowledgement

We thank the National Science Council of Taiwan for the ﬁnancial support and the National High Perform-ance Computing Center of Taiwan for supporting data-bank searching.

Appendix A. Supplementary material

Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic

Data Centre, CCDC nos. 234583–234585 and 243419. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1 EZ, UK (fax: +44-1223-336033;

e-mail: deposit@ccdc.cam.ac.uk or

http://www.ccdc.ca-m.ac.uk). Data for theoretical calculation can be ob-tained from the author by request via e-mail at juihuang@cc.ncue.edu.tw. Supplementary data associ-ated with this article can be found, in the online version, atdoi:10.1016/j.jorganchem.2004.07.046.

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Table 2

Crystallographic data and reﬁnement for compounds 1, 2, 3 and 4

1 2 3 4

Formula C22H42HfN6 C36H52HfN8O2 C40H56HfN8O3 C44H60HfN8O4

Fw 569.11 807.35 875.42 943.49

Temperature (K) 293(2) 150(2) 150(1) 150(2)

Crystal system Monoclinic Monoclinic Monoclinic Monoclinic

Space group P21/c P21/c P21/c Cc a (A˚ ) 10.022(3) 15.548(4) 11.1338(1) 11.4627(15) b (A˚ ) 16.370(4) 10.867(3) 23.5981(3) 16.219(2) c (A˚ ) 15.515(4) 21.237(5) 15.1340(2) 23.993(3) b(°) 104.020(4) 94.427(4) 105.8891(5) 100.622(2) V (A˚3) 2469.4(11) 3577.5(14) 3824.33(8) 4384.1(10) Z 4 4 4 4 Dcalc(g/cm3) 1.531 1.499 1.520 1.429 F(0 0 0) 11 52 1648 1792 1936 hRange (°) 1.84–27.58 1.31–27.55 1.64–25.00 1.73–27.53

No. of reﬂections collected 15 560 24 310 30 498 21 771

No. of independent reﬂections (Rint) 5657 (0.0374) 8142 (0.1254) 6728 (0.0619) 9677 (0.0317)

No. of parameters 270 424 469 514

Goodness of ﬁt on F2 0.848 0.898 1.127 0.921

Final R, wR2[I > 2r(I)] 0.0221, 0.0388 0.0606, 0.1582 0.0543, 0.1414 0.0263, 0.0544

R, wR2(all data) 0.0338, 0.0401 0.1205, 0.1834 0.0856, 0.1691 0.0307, 0.0544

(8)

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