Effect of solvent on reactions of Cp2Zr{(μ-H)2BHR}2 and Cp2ZrH{(μ-H)2BHR} (R = CH3, Ph) with B(C6F5)3

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Eﬀect of solvent on reactions of Cp

2

Zr{(l-H)

2

BHR}

2

and

Cp

2

ZrH{(l-H)

2

BHR} (R = CH

3

, Ph) with B(C

6

F

5

)

3 Fu-Chen Liu

a,*

, Shou-Chon Chen

a

, Gene-Hsian Lee

b

, Shie-Ming Peng

b

a_{Department of Chemistry, National Dong Hwa University, Hualien 974, Taiwan, ROC} b_{Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, ROC}

Received 4 November 2006; received in revised form 5 February 2007; accepted 9 February 2007 Available online 25 February 2007

Abstract

The eﬀect that a solvent has on reactions of Cp2Zr{(l-H)2BHR}2and Cp2ZrH{(l-H)2BHR} (R = CH3, Ph) with B(C6F5)3has been

studied. From the reaction in benzene the metathesis product Cp2Zr{(l-H)2B(C6F5)2}2, 2, was isolated. In the case of diethyl ether,

dif-ferent hydride abstraction products, including [Cp2Zr(OEt2){(l-H)2BHPh}][HB(C6F5)3], 3, [Cp2Zr(OEt2){(l-H)2BHCH3}][HB(C6F5)3],

4, [Cp2Zr(OEt2){(l-H)2BH2}][HB(C6F5)3], 5, and [Cp2Zr(OEt)(OEt2)][HB(C6F5)3], 6, were isolated depending on the starting

zircono-cene complex. The diethyl ether molecules of 3–6 are weakly coordinated to Zr and displaced in THF solution. Isolation of 3 and 4 is attributed to their fast precipitation from the reaction mixture, which prevented further reactions from occurring. In addition to the hydride abstraction, a hydride metathesis was also involved in the formation of 5. Time-elapsed11B NMR studies indicate that 3 and 4 are the intermediates on the pathway to 5 and 6. The molecular structures of 2–6 were determined by single-crystal X-ray diﬀraction.

Keywords: Organotrihydroborate; Metathesis; Hydride abstraction

1. Introduction

Recently there has been an increased interest in the prep-aration of metallocene cations of the ½Cp0

2MR þ

type (Cp0_{= C}

5H5, C5Me5; M = Zr, Ti), due to their catalytic

activity in Ziegler–Natta oleﬁn polymerization [1]. Although in rare cases these 14e cationic species have been isolated, preparation of THF adducts of ionic com-pounds ½Cp02MR

þ

½X (X = BPh4, BR(C6F5)3) is much

more common[2]. The catalytic ability of [Cp2ZrR(THF)]+

has been studied [3]. In addition to the alkyl carbanion abstraction to form a cation, the Lewis acid B(C6F5)3can

also abstract a terminal hydride from a metallocene hydride or a bridging hydrogen M–H–B from a metallo-cene organohydroborate complex. Marks and co-workers showed that abstraction of a hydride from Cp₂ZrH2

by B(C6F5)3 results in the ionic compound ½Cp2

ZrH-½HBðC6F5Þ3 [4]. Several examples of hydride abstraction

from metallocene cyclic organodihydroborates using

B(C6F5)3 have been reported by Shore and co-workers.

These reactions have been shown to be solvent-dependent, with diﬀerent products being isolated from non-coordinat-ing and coordinatnon-coordinat-ing solvents. In the case of toluene, a non-coordinating solvent, B(C6F5)3 removed the hydride

from Cp2ZrH{(l-H)2BR} (R = C4H8, C5H10) yielding a

single hydrogen-bridged compound [(l-H){Cp2

Zr(l-H)2BR}2][HB(C6F5)3]. From diethyl ether, a coordinating

solvent, the ethoxy-substituted compound [Cp2

Zr(OE-t2)(OEt)][HB(C6F5)3] was isolated [5]. On the other hand,

reactions of titanium compounds Cp2Ti{(l-H)2BR}

(R = C4H8, C5H10, C8H14) with B(C6F5)3 furnished a

metathesis product Cp2Ti{(l-H)2B(C6F5)2} in toluene

and the ionic compound [Cp2Ti(OEt2)2][HB(C6F5)3] in

ether [6]. A more complicated result was obtained when Cp2Nb{(l-H)2BR} (R = C4H8, C5H10, C8H14) was reacted

*

Corresponding author. Tel.: +886 3 8633601; fax: +886 3 8633570. E-mail address:fcliu@mail.ndhu.edu.tw(F.-C. Liu).

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with B(C6F5)3. In toluene the ionic compound [Cp2 Nb(l-H)(g5-g1-C5H4)Nb(g 5 -g1-C5H4)2Nb{(l-H)(g 5 -g1-C5H4

B-(C6F5)2)}][HB(C6F5)3] formed, however, the neutral

compound CpNb(B(C6F5){(l-H)(g5-C5H4B(C6F5)2)}) was

obtained from the reaction in ether[7]. It has been reported in our recent study that several group 4 metallocene organ-otrihydroborate compounds display properties diﬀerent from those of their cyclic organodihydroborate analogs [8]. For the purpose of further comparison of the metallo-cene organodihydroborate and the organotrihydroborate complexes, we were interested in reactions of complexes of the latter type with B(C6F5)3. In this contribution, we

report on the recent results obtained from the studies of reactions of Cp2Zr{(l-H)2BHR}2 and Cp2

ZrH{(l-H)2BHR} (R = CH3, Ph) with B(C6F5)3 in both benzene

and diethyl ether. 2. Results and discussion

2.1. Formation and properties of Cp2ZrH{(l-H)2BHCH3}

(1), Cp2Zr{(l-H)2B(C6F5)2}2(2), [Cp2Zr(OEt2){(l-H)2

BHPh}][HB(C6F5)3] (3), [Cp2Zr(OEt2){(l-H)2

-BHCH3}][HB(C6F5)3] (4), [Cp2Zr(OEt2){(l-H)2

-BH2}][HB(C6F5)3] (5), and [Cp2Zr(OEt)

(OEt2)][HB(C6F5)3] (6)

Previously compound Cp2ZrH{(l-H)2BHCH3}, 1, has

been prepared in low yield through the reaction of Cp2ZrCl2 with excess amount of LiBH3CH3 followed by

sublimation[9]. NMR studies from our group have shown that 1 is a product of Cp2Zr{(l-H)2BHCH3}2

decomposi-tion[8], however, it is not practical to use this as a method for a large scale preparation of 1. Thus, compound 1 was prepared from the reaction of Cp2Zr{(l-H)2BHCH3}2with

N(C2H5)3in ether according to Eq.(1). The ease of the

by-product CH3BH2ÆN(C2H5)3 removal under a dynamic

vacuum and the high isolated yield of 1 are the distinct advantages of this method.

The reactions of either Cp2Zr{(l-H)2BHR}2 or

Cp2ZrH{(l-H)2BHR} (R = CH3, Ph) with B(C6F5)3 in

benzene yielded compound Cp2Zr{(l-H)2B(C6F5)2}2, 2

according toScheme 1. Two equivalents of B(C6F5)3were

used in the case of bis(organohydroborate) compounds Cp2Zr{(l-H)2BHR}2, however, 3 equiv. of B(C6F5)3were

required in the case of zirconium hydride compounds Cp2ZrH{(l-H)2BHR}. Under these conditions, 2 is a

major product along with several unidentiﬁed species, which are soluble in benzene and characterized by singlet

signals in 11B NMR. Compound 2 has been previously

prepared by Piers and co-workers [10] from the reaction of Cp2Zr(CH3)2with HB(C6F5)2in benzene. Overall, our

data obtained for 2 are consistent with those reported by Piers, except for the IR data displaying an additional strong absorption band at 1475 cm1 in KBr compared with the literature spectrum acquired in Nujol. This dis-crepancy could be explained taking into account that Nujol itself has a strong broad absorption band at 1460 cm1.

Competing reactions took place when Cp2

Zr{(l-H)2BHR}2 and Cp2ZrH{(l-H)2BHR} (R = CH3, Ph)

were mixed with B(C6F5)3 in diethyl ether. [Cp2

Zr-(OEt2){(l-H)2BHPh}][HB(C6F5)3], 3, [Cp2Zr(OEt2

){(l-H)2BHCH3}][HB(C6F5)3], 4, [Cp2Zr(OEt2){(l-H)2BH2

}]-[HB(C6F5)3], 5, and [Cp2Zr(OEt)(OEt2)][HB(C6F5)3], 6,

were the major products resulting from the hydride abstraction (Scheme 2). Thus, B(C6F5)3removed the

termi-nal hydride from Cp2ZrH{(l-H)2BHPh} producing

com-pound 3 (path a). A similar product, comcom-pound 4, was isolated according to path b. In contrast, reactions of Cp2Zr{(l-H)2BHPh}2 and Cp2ZrH{(l-H)2BHCH3} with

B(C6F5)3 produced compounds 5 (path c) and 6 (path d),

respectively. Compound 6, which is also a major by-prod-uct of reactions shown in paths a–c, can be isolated from reactions of Cp2Zr(l-H)2BHR}2 (R = CH3, Ph) and

Cp2ZrH(l-H)2BHPh} with two-fold excess of B(C6F5)3in

diethyl ether, as described in the experimental section. The role of excess B(C6F5)3is to accelerate the formation

of 6, since compound 6 becomes a major product of reac-tions shown in paths a and b at prolonged stirring. These cationic species were isolated using crystallization. Crystals of 3 and 4 are slightly soluble in ether; however, those of 5 and 6 are practically insoluble.

Using d8-THF as a solvent to acquire the1H NMR

spec-tra of compounds 3–5 resulted in displacement of the coor-dinated ether molecules by those of the deuterated solvent. Two broad signals corresponding to the hydrogens on boron atoms were observed. Thus, the terminal hydrogen of the anion appeared at 3.74 ppm for each compound,

CH3BH2 N(C2H5)3 Zr H CH3 H B H H H B H CH3 + Zr H CH3 H B H H N(C2H5)3 + ether

_.

1 ð1Þ

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as previously reported for 6[5a]. In contrast, for the cat-ionic part the chemical shift depends on the substituent on the boron atom. Thus, the cationic borohydride signals for 3–5 appear at 1.20, 0.65, and 0.85 ppm, respectively. Due to the fast exchange of bridging and terminal hydro-gen atoms on the NMR timescale, only one cationic boro-hydride signal was observed for each complex. Two boron signals, a broad quartet and a doublet, were observed in the 11B NMR spectra of 3–5. The doublet appearing at about26 ppm (JB–H= 93 Hz) was assigned to the anion

[HB(C6F5)3]. The boron chemical shifts of cations of

3–5 and their THF coordinated analogs are listed inTable 1. The chemical shifts of [Cp2Zr(OEt2){(l-H)2BH2}]+ was

recorded during the reaction. In THF the coordinated ether was replaced by THF resulting in [Cp2

Zr(THF){(l-H)2BHR}]+ cations. Although a boron chemical shift

could diﬀer slightly from one solvent to another, Table 1 indicates that all of the THF-coordinated compounds dis-play upﬁeld chemical shifts compared with their ether-coordinated counterparts. Since THF is a stronger electron

Zr H H B C₆F₅ C6F5 Zr H Ph H B H H H B H Ph C6F5 C₆F₅ H B H Zr H CH3 H B H H H B H CH₃ Zr H CH₃ H B H H Zr H Ph H B H H 2 B(C₆F₅)₃ benzene benzene benzene benzene 2 B(C6F5)3 3 B(C₆F₅)₃ 3 B(C6F5)3 2 Scheme 1. Zr H Ph H B H H H B H Ph Zr H CH3 H B H H H B H CH3 B(C6F5)3 ether Zr OC4H10 + B H H H H Zr OC4H10 + B H H H Ph Zr B H H H Ph H Zr B H H H CH3 H Zr OC2H5 OC4H10 + Zr OC4H10 HB(C6F5)3 + B H H H CH3 HB(C6F5)3 HB(C6F5)3 HB(C6F5)3 ether B(C6F5)3 3 4 6 5 ether B(C6F5)3 ether B(C6F5)3

a

b

c

d

Scheme 2.

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donor than ether, it provides more electron density to the metal. Thus, the electron deﬁciency of the metal is allevi-ated resulting in the increased electron density on the boron atom and an upﬁeld boron chemical shift.

Formation of 5 involves both a hydride abstraction and a hydride metathesis reaction. The time-elapsed11B NMR study of the reaction of Cp2Zr{(l-H)2BHPh}2 with

B(C6F5)3(Supplementary material Fig. S5) suggests

com-pound 3 is the intermediate of the reaction. As time elapsed, colorless crystals of [Cp2Zr(OEt2){(l-H)2BH2

}]-[HB(C6F5)3] began to form while compound 3 gradually

disappeared. The reaction occurred in a stepwise fashion. In the ﬁrst step, Cp2Zr{(l-H)2BHPh}2 reacted with

B(C6F5)3to produce compound 3 and the organodiborane

‘‘(BH2Ph)2’’. Consequent metathesis reaction of this

organodiborane or a product related to it with compound 3 produced compound 5 and triphenylborane B(C6H5)3.

Formation of 5 is unique as the outcome of this type has never been observed in reactions of B(C6F5)3 with other

organohydroborate complexes. In contrast, the reverse process, alkyl metathesis, has been reported by Schlesinger [11]and Marks[12]in their preparations of organohydrob-orate uranium complexes.

Compound 6 has been prepared from the reaction of Cp2ZrH{(l-H)2BR} (R = C4H8, C5H10) with B(C6F5)3

[5]. A mechanism has been proposed for this reaction [13], however, no detailed NMR study has been performed.

The time-elapsed 11B NMR study of the reaction of

Cp2ZrH{(l-H)2BHCH3} with B(C6F5)3 (Supplementary

material Fig. S6) suggests compound 4 is an intermediate in this reaction. Compound 4 formed in the beginning of the reaction. As time elapsed, compound 4 disappeared and crystals of compound 6 formed gradually inside the NMR tube. This result conﬁrms the mechanism proposed previously[13].

The time-elapsed 11B NMR studies suggest that com-pounds 3 and 4 are intermediates on the pathway to 5 and 6. The key point to their successful isolation from reac-tions illustrated inScheme 2is their fast precipitation from the reaction mixtures, which prevents further reactions from occurring. However, under the conditions of reac-tions illustrated in paths c and d, compounds 3 and 4 did not precipitated immediately as they were forming, thus providing an opportunity for isolation of 5 and 6 due to further transformations.

2.2. Molecular structures

The molecular structures of 2–6 were determined by sin-gle-crystal X-ray diffraction analysis. The crystals of 2 iso-lated from an ether solution contain the solvent of crystallization. The cell parameters obtained for 2 are slightly different from those reported by Piers and co-work-ers[10a] for the compound isolated from a benzene solu-tion. Two molecules of 2 with slightly different bond distances and angles were found in the unit cell, and one of them is shown inFig. 1. Comparison of their bond dis-tances and angles with those for 2 isolated from benzene is

presented in Table 2. Although the Zr–B distances

(2.652(3) and 2.658(3) A˚ ) for 2 isolated in this work are slightly shorter than that reported in literature (2.696(10) and 2.679(10) A˚ ) [10a], compound 2 still has the longest reported Zr–H–B bond distance. Zr–H and B–H distances as well as the related bond angles reported here are more precise due to the fact that it was possible to locate and reﬁne the bridging hydrogens of 2.

The molecular structures of cations of compounds 3–5 are shown inFigs. 2–4. The corresponding crystallographic data, selected bond distances and bond angles are given in Tables 3–6. The molecular structure of 6 has been reported [5], the crystallographic data are included in the Supple-mentary material. The coordination geometries around zir-conium atoms of 3–5 are the same and can be described best as distorted tetrahedrons. At the corners of a tetrahe-dron are the centers of two Cp rings, an oxygen atom, and a boron atom connected to the zirconium atom through two bridging hydrogens. For compound 4 two independent molecules were found in the unit cell. These two molecules have slightly diﬀerent bond distances and angles, and only one molecular structure is presented. The hydrogens bound to the boron atoms were located and reﬁned isotropically. The Zr–B distances are 2.561(5) A˚ in 3, 2.514(12) and

Fig. 1. Molecular structure of Cp2Zr{(l-H)2B(C6F5)2} Æ OC4H10showing

30% probability thermal ellipsoids. Table 1

The boron chemical shift (ppm) of the cation in (3)–(5) and their THF coordinated analogs [Cp2Zr(OEt2){(l-H)2BHR}]+ in ether [Cp2Zr(THF){(l-H)2 -BHR}]+in THF R = Ph (3) 13.75 11.90 R = CH3 (4) 15.77 13.34 R = H (5) 4.33 2.08

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2.575(12) A˚ in 4, and 2.531(13) A˚ in 5. Compared with the Zr–B distances of the neutral alkylborate complexes found in the range of 2.538–2.696 A˚ [8,14], these cationic Zr–B distances are either shorter than, or falling into the above range for neutral compounds closer to its lower limit. The cationic character alone can not account for these short distances. Although the average Zr–B distance found in 4 is shorter than that found in Cp2ZrH{(l-H)2BHCH3}

(2.558(4) A˚ ) [9], the Zr–B distance in 3 is longer than that found in the corresponding zirconium hydride Cp2ZrH{(l-H)2BHPh} (2.538(11) A˚ ) [14]. Indeed, the

steric eﬀect also have to be considered. The cation

[(C5H4Me)2Zr(THF){(l-H)2BH2}]+ (2.54(1) A˚ , 2.55(1) A˚)

[15] is more crowded than that in 5 and displays a longer Zr–B distance. The Zr–O distances are 2.263(3) A˚ in 3, 2.243(5) and 2.261(5) A˚ in 4, and 2.253(5) A˚ in 5. These Zr–O distances are longer than those found in [Cp2Zr(CH3)(THF)]+ (2.122(14) A˚ ) [16], [(C5H4Me)2 -Zr(THF){(l-H)2BH2}]+ (2.239(5), 2.231(6) A˚ ) [15], [Cp2Zr(OBut)(THF)]+(2.200(4) A˚ )[17], [Cp2ZrCl(OEt2)]+ (2.211(3) A˚ ) [14], [Cp2Zr(OEt)(OEt2)] + (2.209(8) A˚ ) [5a], and the sum of the corresponding covalent radii (2.16 A˚ ) [18]. This result is consistent with a weak coordinating abil-ity of ether observed in the NMR study, where THF was found to be capable of displacing all coordinated ether molecules from the Zr inner coordination sphere. In these ether-coordinated cations, the ether ligand is oriented almost in the plane deﬁned by boron, zirconium and oxy-gen atom of the ether molecule. The C–O–C angles of the ether ligand are similar to each other and falling in the range of 112.1–113.0.

Table 2

Selected interatomic distances (A˚ ) and bond angles () for Cp2

Zr{(l-H)2B(C6F5)2}2ÆC6H6and Cp2Zr{(l-H)2B(C6F5)2}2ÆOC4H10(2) Cp2Zr{(l-H)2 -B(C6F5)2}2ÆC6H6a Cp2Zr{(l-H)2 -B(C6F5)2}2ÆOC4H10 (20) (200) Zr–Hbridge 2.043 2.12(2) 2.12(2) 2.054 2.12(2) 2.14(2) 2.177 1.991 B–Hbridge 1.234 1.19(2) 1.17(2) 1.193 1.17(2) 1.13(2) 1.295 1.243 Zr–B 2.696(10) 2.652(3) 2.658(3) 2.679(10) B(1)–C(7) 1.63(1) 1.620(3) 1.607(3) 1.60(1) 1.608(4) 1.611(4) 1.61(1) 1.62(1) Hbridge–Zr–Hbridge 50.30 51.2(9) 49.3(9) 54.19 Hbridge–B–Hbridge 91.65 101.9(17) 101.8(17) 97.32 C(1)–B(1)–C(7) 113.5(7) 112.4(2) 112.6(2) 113.2(7) a

From Ref.[10a].

Fig. 2. Molecular structure of the cation in [Cp2Zr(OEt2

){(l-H)2BHPh}][HB(C6F5)3] (3), showing 30% probability thermal ellipsoids.

){(l-H)2BHCH3}][HB(C6F5)3] (4), showing 30% probability thermal ellipsoids.

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3. Experimental 3.1. General procedures

All manipulations were carried out on a standard high vacuum line or in a drybox under the atmosphere of nitro-gen. Unless noted otherwise, reagents were used as obtained from the commercial suppliers. The solvents were dried and freshly distilled prior to use. Cp2Zr{(l-H)2BHCH3}2 [8],

Cp2Zr{(l-H)2BHPh}2Æ(1/2 toluene)[14], and Cp2

ZrH{(l-H)2BHPh} [14] were prepared according to the literature

methods. Elemental analyses were recorded on a Hitachi 270–30 spectrometer. Proton spectra (d(TMS) 0.00 ppm) were recorded on a Bruker Avance DPX300 spectrometer operating at 300.132 MHz. 11B spectra (externally refer-enced to BF3ÆOEt2(d 0.00 ppm)) were recorded on a

Var-ian Unity Inova 600 operating at 192.481 MHz, or on a

Bruker Avance DPX300 spectrometer operating at

96.294 MHz. Infrared spectra were recorded on a Jasco FT/IR-460 Plus spectrometer with 2 cm1resolution. 3.2. X-ray crystal structure determination

Suitable single crystals were mounted and sealed inside glass ﬁbers under nitrogen. Crystallographic data

collec-tions were carried out on a Nonius KappaCCD diffractom-eter with graphite monochromated Mo Ka radiation (k = 0.71073 A˚ ) at 150(1) K. Cell parameters were retrieved and refined usingDENZO-SMN[20]software on all reflections.

Data reduction was performed using the DENZO-SMN [20]

software. An empirical absorption correction was based on the symmetry-equivalent reﬂections and was applied to the data using theSORTAV [21]program. Structure

anal-ysis was performed using SHELXTL program on a personal

computer. Structures were solved using theSHELXS-97[22]

program and reﬁned using SHELXL-97 [23] program by

full-matrix least-squares on F2 values. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms attached to the borons were located from the d-Fourier map and refined isotropically. Hydrogen atoms attached to the carbons were fixed at calculated positions and refined using a riding mode. Detailed crystallographic data are listed inTable 3.

3.3. Preparation of complexes 3.3.1. Cp2ZrH{(l-H)2BHCH3} (1)

Cp2Zr{(l-H)2BHCH3}2 (922.1 mg, 3.3 mmol) and

about 15 mL of diethyl ether were added into a ﬂask. After degassing, a 0.46 mL (3.3 mmol) of N(C2H5)3 was

trans-Table 3

Crystallographic data for Cp2Zr{(l-H)2B(C6F5)2}2ÆOC4H10 (2), [Cp2Zr(OEt2){(l-H)2BHPh}][HB(C6F5)3] (3), [Cp2Zr(OEt2){(l-H)2

-BHCH3}][HB(C6F5)3] (4), and [Cp2Zr(OEt2){(l-H)2BH2}][HB(C6F5)3] (5)

Empirical formula C38H24B2F20OZr C38H29B2F15OZr C33H27B2F15OZr C32H25B2F15Ozr

Fw 989.41 899.45 837.39 823.36

T (K) 150(1) 150(1) 150(1) 150(1)

Crystal system Monoclinic Monoclinic Triclinic Monoclinic

Space group C2/c P21/c P 1 P21/n a (A˚ ) 23.0148(12) 11.8403(5) 12.7385(6) 12.6640(5) b (A˚ ) 17.9319(9) 13.0180(6) 12.8112(5) 20.7530(8) c (A˚ ) 20.7311(10) 23.8777(10) 20.6137(8) 12.8779(5) a() 91.360(1) b() 114.033(1) 95.873(1) 91.497(1) 104.117(1) c() 102.673(1) V (A˚3) _7814.0(7) _3661.1(3) _3279.5(2) _3282.3(2) Z 8 4 4 4 qcalcd(g/cm 3 ) 1.682 1.632 1.696 1.666 Crystal size (mm) 0.40· 0.40 · 0.30 0.25· 0.20 · 0.20 0.12· 0.10 · 0.10 0.25· 0.10 · 0.10 Radiation (k, A˚ ) Mo Ka (0.71073) Mo Ka (0.71073) Mo Ka (0.71073) Mo Ka (0.71073) 2h Limits () 1.49–27.50 1.71–27.50 0.99–25.00 1.90–25.00 Index ranges 29 6 h 6 29, 15 6 h 6 15, 15 6 h 6 15, 15 6 h 6 15, 23 6 k 6 23, 16 6 k 6 16, 15 6 k 6 15, 23 6 k 6 24, 19 6 l 6 26 31 6 l 6 30 24 6 l 6 24 15 6 l 6 15 Reﬂections collected 31 341 35 145 29 441 26 618 Unique reﬂections 8970 8397 11 543 5769

Unique reﬂections [I > 2.0r(I)] 3920 1800 1672 1640

Completeness to h (%) 100.0 100.0 100.0 100.0 l(mm1) 0.409 0.409 0.449 0.447 Maximum/minimum transmissions 0.9227, 0.9047 0.9566, 0.8964 Data/restraints/parameters 8970/0/572 8397/0/526 11543/4/953 5769/0/470 R1a[I > 2.0r(I)] 0.0403 0.0700 0.0890 0.0972 wR2b(all data) 0.1061 0.1545 0.1548 0.1911 Rint 0.0335 0.0723 0.0951 0.0842 GOF on F2 1.033 1.117 1.106 1.264 a _R 1=PiFoi jFci/PiFoj. b wR2¼ fPwðF2o F2cÞ 2 =PwðF2 oÞ 2 g1=2.

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ferred into the ﬂask at 78 C. The ﬂask was gradually warmed to room temperature resulting in a clear solution. After stirring for 4 h, the volatile species were removed

under a dynamic vacuum, and the resulting white solid was redissolved in ether and kept at35 C until crystalli-zation occurred. Isolation of crystalline material resulted in 696.0 mg of Cp2ZrH{(l-H)2BHCH3} (84% yield)[9].

3.3.2. Cp2Zr{(l-H)2B(C6F5)2}2Æ (C6H6) (2)

Method 1. In a drybox Cp2Zr{(l-H)2BHCH3}2(141.7 mg,

0.5 mmol) and B(C6F5)3(516.0 mg, 1.0 mmol)

were placed into a flask. The flask was evacu-ated, and approximately 20 mL of benzene was transferred into the flask at 78 C. The flask was gradually warmed to room tempera-ture and kept at room temperatempera-ture overnight. Fine crystals of Cp2Zr{(l-H)2B(C6F5)2}2Æ

(C6H6)[10]formed. The solution was removed,

and the crystals were washed with two portions of 5 mL of benzene and dried under vacuum. The title compound was isolated as ﬁne crystals (320.0 mg, 64% yield).

Method 2. Using Cp2Zr{(l-H)2BHPh}2Æ(1/2 toluene)

(225.0 mg, 0.50 mmol), B(C6F5)3 (511.2 mg,

1.0 mmol) and 25 mL of benzene in a proce-dure similar to the one described in method 1 furnished 260.0 mg (52% yield) of ﬁne crys-tals of the title compound.

Method 3. Using Cp2ZrH{(l-H)2BHCH3} (84.0 mg, 0.33

mmol), B(C6F5)3 (510.0 mg, 1.0 mmol) and

10 mL of benzene in a procedure similar to the one described in method 1 yielded 160.0 mg (49% yield) of ﬁne crystals of the title compound.

Method 4. Using Cp2ZrH{(l-H)2BHPh} (157.0 mg, 0.5

10 mL of benzene in a procedure similar to

Table 6

Selected interatomic distances (A˚ ) and bond angles () for [Cp2Zr(OEt2){(l-H)2BH2}][HB(C6F5)3] (5) Bond lengths av Zr–C(1–5)a 2.48[1] Zr–H(1B) 2.00(10) av Zr–C(6-10)a 2.50[1] B(1)–H(1D) 1.04(10) Zr–B(1) 2.531(13) B(1)–H(1B) 1.17(10) Zr–O(1) 2.253(5) B(1)–H(1C) 1.24(10) Zr–H(1A) 1.86(10) B(1)–H(1A) 1.29(10) Angles H(1A)–Zr–H(1B) 56(4) H(1B)–B(1)–H(1A) 95(6) H(1D)–B(1)–H(1B) 122(8) H(1C)–B(1)–H(1A) 104(6) H(1D)–B(1)–H(1C) 124(7) C(11)–O(1)–C(13) 113.0(6) H(1B)–B(1)–H(1C) 105(7) C(11)–O(1)–Zr 120.7(5) H(1D)–B(1)–H(1A) 101(7) C(13)–O(1)–Zr 123.7(5)

a _{The standard derivation (r}

l) for the average bond length of Zr–C is

calculated according to the equations[19] hli ¼ Rmlm=m;

rl¼ ½Rmðlm hliÞ 2

=ðmðm 1ÞÞ1=2;

whereÆlæ is the mean length, lmis the length of the mth bond, and m is the

number of bonds. Table 4

Selected interatomic distances (A˚ ) and bond angles () for [Cp2Zr(OEt2){(l-H)2BHPh}][HB(C6F5)3] (3) Bond lengths av Zr–C(7-11)a 2.49[1] Zr–H(1B) 2.10(5) av Zr–C(12-16)a _2.497_[4] _B(1)–H(1C) _1.13(5) Zr–B(1) 2.561(5) B(1)–H(1B) 1.20(5) Zr–O(1) 2.263(3) B(1)–H(1A) 1.28(4) Zr–H(1A) 1.92(4) Angles H(1A)–Zr–H(1B) 55.3(19) H(1B)–B(1)–C(1) 111(2) H(1C)–B(1)–H(1B) 114(3) H(1A)–B(1)–C(1) 110(2) H(1C)–B(1)–H(1A) 108(3) C(19)–O(1)–C(17) 112.1(3) H(1B)–B(1)–H(1A) 98(3) C(19)–O(1)–Zr 119.3(2) H(1C)–B(1)–C(1) 114(3) C(17)–O(1)–Zr 125.4(2)

=ðmðm 1ÞÞ1=2

;

number of bonds.

Table 5

Selected interatomic distances (A˚ ) and bond angles () for [Cp2Zr(OEt2){(l-H)2BHCH3}][HB(C6F5)3] (4) Bond lengths av Zr(1)–C(6–10)a _2.47_[1] _{av Zr(2)–C(21–25)}a _2.479_[7] av Zr(1)–C(11–15)a _2.48_[1] _{av Zr(2)–C(26–30)}a _2.47_[1] Zr(1)–B(1) 2.514(12) Zr(2)–B(2) 2.575(12) Zr(1)–O(1) 2.243(5) Zr(2)–O(2) 2.261(5) Zr(1)–H(1A) 1.95(8) Zr(2)–H(2A) 1.92(9) Zr(1)–H(1B) 1.97(8) Zr(2)–H(2B) 1.95(9) B(1)–H(1B) 1.13(9) B(2)–H(2C) 1.19(9) B(1)–H(1A) 1.17(8) B(2)–H(2A) 1.201(10) B(1)–H(1C) 1.27(8) B(2)–H(2B) 1.204(11) Angles H(1A)–Zr(1)–H(1B) 53(3) H(2A)–Zr(2)–H(2B) 51.4(15) H(1B)–B(1)–H(1A) 98(6) H(2C)–B(2)–H(2A) 92(6) H(1B)–B(1)–H(1C) 98(6) H(2C)–B(2)–H(2B) 96(6) H(1A)–B(1)–H(1C) 100(5) H(2A)–B(2)–H(2B) 89(6) H(1B)–B(1)–C(1) 113(4) H(2C)–B(2)–C(16) 132(5) H(1A)–B(1)–C(1) 122(4) H(2A)–B(2)–C(16) 126(5) H(1C)–B(1)–C(1) 121(4) H(2B)–B(2)–C(16) 111(5) H(1A)–Zr(1)–O(1) 72(2) H(2A)–Zr(2)–O(2) 125.3(11) H(1B)–Zr(1)–O(1) 123(3) H(2B)–Zr(2)–O(2) 74.4(13) C(4)–O(1)–C(2) 112.6(7) C(19)–O(2)–C(17) 112.7(5) C(4)–O(1)–Zr(1) 125.7(5) C(19)–O(2)–Zr(2) 123.5(4) C(2)–O(1)–Zr(1) 119.9(5) C(17)–O(2)–Zr(2) 121.8(4)

=ðmðm 1ÞÞ1=2

;

(8)

the one described in method 1 aﬀorded 234.0 mg (47% yield) of ﬁne crystals of the title compound.11B NMR (benzene): d13.4 ppm (t, JB–H= 64 Hz).1H NMR (C6D6): d 5.38 (s, 10H, Cp), 0.40 ppm (br, q, 4H, l-H). IR(KBr): 3130(br, vw), 2357(br, vw), 2318(br, vw), 2183(br, w), 2112(br, w), 2027(br, vw), 1643(m), 1514(s), 1475(vs), 1379(vw), 1333(w), 1288(m), 1261(m), 1112(m), 1097(m), 1012(vw), 989(vw), 955(m), 920(vw), 885(w), 858(vw), 827(m), 756(vw), 720(vw), 687(w), 625(vw), 606(vw), 563(vw) cm1. C40H20B2F20Zr: C, 48.36; H, 2.03. Found: C, 48.44; H, 2.03%. 3.3.3. [Cp2Zr(OEt2){(l-H)2BHPh}][HB(C6F5)3] (3)

In a drybox a 50 mL ﬂask was charged with 101.7 mg

(0.32 mmol) of Cp2ZrH{(l-H)2BHPh} and 166.2 mg

(0.32 mmol) of B(C6F5)3. The ﬂask was evacuated, and

about 10 mL of the diethyl ether was condensed into it at 78 C. The ﬂask was warmed to room temperature fol-lowed by stirring of the reaction mixture for 4 h. A white solid was obtained after removal of the solvent. The solid was redissolved in diethyl ether and layered with hexane. The title compound was obtained as colorless crystals (190 mg, 66% yield). 11B NMR (d8-THF): d 11.90 (br), 26.16 ppm (d, JB–H= 93 Hz).11B NMR (ether): d 13.75 (br), 25.43 ppm (d, JB–H= 90 Hz). 1H NMR (d8-THF): d 7.39–7.20 (m, 5H, Ph), 6.70 (s, 10H, Cp), 3.74 (br, q, 1H, HB), 3.39 (q, 4H, ether), 1.20 (br, 3H, H3B), 1.12 ppm (t, 6H, ether). IR(KBr): 3072(vw), 3033 (vw), 2999(vw), 2976(w), 2931(w), 2900(w), 2870(w), 2816(vw), 2345(s), 2220(w), 2195(s), 2148(vw), 1942(vs), 1840(vs), 1736(vw), 1639(vw), 1483(s), 1450(w), 1417 (w), 1383(vw), 1369(vw), 1340(vw), 1288(vw), 1234(vw), 1188(w), 1122(s), 1028(vw), 947(m), 935(w), 858(w), 796(vw), 637(vw), 611(vw), 578(vw), 565(vw), 517

(w), 494(vw), 472(vw), 409(vw) cm1. Anal. Calc. for C38H29B2F15OZr: C, 50.74; H, 3.25. Found: C, 50.60; H,

3.24%.

3.3.4. [Cp2Zr(OEt2){(l-H)2BHCH3}][HB(C6F5)3] (4)

Cp2Zr{(l-H)2BHCH3}2 (140.2 mg, 0.5 mmol) and

B(C6F5)3(257.0 mg, 0.5 mmol) were placed into a reaction

flask. The flask was evacuated, and about 10 mL of diethyl ether was transferred into the flask at78 C. The solution was gradually warmed to room temperature and stirred until it became clear. Crystals of [Cp2Zr(OEt2

){(l-H)2BHCH3}][HB(C6F5)3] grew slowly from this solution.

After standing at room temperature overnight, the ether solution was removed, and the crystals were washed twice with 10 mL portions of cold ether and dried under vacuum. The title compound was obtained as colorless crystals (290.0 mg, 69.3% yield). 11B NMR (THF): d 13.34 (br), 26.57 ppm (d, JB–H= 93 Hz).11B NMR (ether): d 15.77 (br, q), 25.36 ppm (d, JB–H= 90 Hz). 1H NMR (d8 -THF): d 6.70 (s, 10H, Cp), 3.75 (br, q, 1H, HB), 3.39 (q, 4H, ether), 1.12 (t, 6H, ether), 0.47 (br, q, JH–H= 3.9 Hz, 3H, CH3), and 0.65 ppm (br, 3H, H3B). IR(KBr): 3118(w), 2983(w), 2943(w), 2904(vw), 2870(vw), 2420(w), 2360(w), 2337(w), 2287(vw), 2027(vw), 1957(vw), 1874(vw), 1639(m), 1603(vw), 1554(vw), 1510(s), 1464(vs), 1412(w), 1392(w), 1377(m), 1302(vw), 1273(m), 1219(vw), 1188(vw), 1113(m), 1103(m), 1068(m), 1016(w), 991(w), 966(s), 908(w), 881(vw), 827(m), 789(vw), 764(m), 725(vw), 660(w), 648(w), 602(vw), 567(vw), and

409(w) cm1. Anal. Calc. for C33H27B2F15OZr: C, 47.33;

H, 3.25. Found: C, 46.94; H, 3.31%.

3.3.5. [Cp2Zr(OEt2){(l-H)2BH2}][HB(C6F5)3] (5)

Using Cp2Zr{(l-H)2BHPh}2Æ(1/2 toluene) (225.0 mg,

0.50 mmol), B(C6F5)3(256.0 mg,0.50 mmol) and 15 mL of

diethyl ether in a procedure is similar to the one describing the preparation of 4 aﬀorded 360.0 mg (87.4% yield) of the title compound as colorless crystals. 11B NMR (THF): d 2.08 (br, quintet), 26.00 ppm (d, JB–H= 92 Hz). 11B NMR (ether): d 4.33 (br),25.14 ppm (d, JB–H= 90 Hz). 1 H NMR (d8-THF): d 6.71 (s, 10H, Cp), 3.72 (br, q, 1H, HB), 3.39 (q, 4H, ether), 1.12 (t, 6H, ether), 0.85 ppm (br, 3H, H3B). IR(KBr): 3119(br, w), 2986(vw), 2486(w), 2426(m), 2376(w), 2270(vw), 2141(w), 2071(vw), 1954(w), 1639(m), 1603(vw), 1549(vw), 1510(s), 1460(vs), 1392 (w), 1377(w), 1344(m), 1317(w), 1273(m), 1184(vw), 1134(m), 1114(m), 1103(m), 1070(m), 1014(m), 991 (w), 966(s), 906(w), 881(vw), 831(m), 796(vw), 762(m), 725(vw), 658(w), 650(w), 603(vw), 569(vw), 518(vw),

469(vw), 446(vw), 423(vw) cm1. Anal. Calc. for

C32H25B2F15OZr: C, 46.58; H, 3.06. Found: C, 46.49; H,

3.01%.

3.3.6. NMR study of the reaction of Cp2Zr{(l-H)2

-BHPh}2Æ (1/2 toluene) with B(C6F5)3in diethyl ether

Cp2Zr{(l-H)2BHPh}2Æ(1/2 toluene) (10.0 mg,

0.022 mmol) and B(C6F5)3 (11.4 mg, 0.022 mmol) were

placed into an NMR tube. After degassing, the diethyl ether was transferred into the tube, and the tube was sealed. After warming it to room temperature a clear solu-tion formed that was monitored by11B NMR.

3.3.7. Blank experiment: [Cp2Zr(OC4H10){(l-H)2

-BHPh}][HB(C6F5)3] and Cp2Zr{(l-H)2BHPh}2Æ (1/2

toluene) in diethyl ether

A reaction ﬂask was charged with 50.0 mg of

[Cp2Zr(OEt2){(l-H)2BHPh}][HB(C6F5)3] and 10.1 mg of

Cp2Zr{(l-H)2BHPh}2Æ(1/2 toluene). After degassing,

about 5 mL of diethyl ether was transferred into the ﬂask at78 C. The ﬂask was warmed to room temperature fol-lowed by stirring for 30 h. The solvent was removed, and the resulting solid was dissolved in THF. The 11B NMR of the solution was acquired. The starting material Cp2Zr{(l-H)2BHPh}2 and a partial decomposition of

[Cp2Zr(OEt2){(l-H)2BHPh}][HB(C6F5)3] with formation

(9)

how-ever, the characteristic signal of the cation [Cp2Zr(OEt2

)-{(l-H)2BH2}] +

was not found.

3.3.8. Preparation of [Cp2Zr(OEt)(OEt2)][HB(C6F5)3]

(6)

Method 1. In a drybox a reaction ﬂask was charged with 225.0 mg of Cp2Zr{(l-H)2BHPh}2Æ(1/2

tolu-ene) (0.5 mmol) and 514.0 mg of B(C6F5)3

(1.0 mmol). The flask was evacuated, and about 10 mL of diethyl ether was transferred into the flask at78 C. The flask was gradu-ally warmed to room temperature, and the reaction mixture was stirred until a clear solu-tion was formed. In the drybox the solvent was allowed to evaporate slowly from the

solution at room temperature yielding

307.0 mg (72% yield) of crystalline title compound.

Method 2. Cp2Zr{(l-H)2BHCH3}2(70.0 mg, 0.25 mmol),

256.0 mg (0.5 mmol) of B(C6F5)3, and 10 mL

of diethyl ether transferred into the flask at 78 C were allowed to warm up to room temperature resulting in a clear solution. The solution was stood aside at room temperature overnight for crystallization. The crystals were filtered off and washed twice with 3 mL por-tions of diethyl ether. A total of 95.0 mg of crystals was obtained. By11B and 1H NMR spectroscopy they were identified as a mixture of [Cp2Zr(OEt2){(l-H)2BHCH3}][HB(C6F5)3]

and [Cp2Zr(OEt)(OEt2)][HB(C6F5)3].

Method 3. Cp2ZrH{(l-H)2BHCH3} (126.2 mg, 0.5

10 mL of diethyl ether were used. The proce-dure was similar to the one described in method 1. After standing at room temperature over-night, the solution turned pink. This solution

was concentrated and kept at 35 C

for crystallization. Pink-colored crystals

(130 mg, 30.5%) were isolated. 11B NMR

spectrum conﬁrmed the formation of [Cp2

Zr-(OEt)(OEt2)][HB(C6F5)3].

3.3.9. NMR study of Cp2ZrH{(l-H)2BHCH3} with of

B(C6F5)3in diethyl ether

Cp2ZrH{(l-H)2BHCH3} (6.2 mg, 0.025 mmol) and

B(C6F5)3(12.6 mg, 0.025 mmol) were added into a NMR

tube. The tube was degassed followed by transfer of about 0.4 mL diethyl ether onto the reagents at78 C. The tube was gradually warmed to room temperature. During the warm-up process, the reaction occurred, and an unidenti-ﬁed gas evolved. The tube was sealed, and the boron spec-tra were acquired.

Acknowledgment

This work was supported by the National Science Coun-cil of the ROC through Grant NSC 94-2113-M-259-007. Appendix A. Supplementary material

CCDC 624286, 624285, 624289, 624287, and 624288, contain the supplementary crystallographic data for 2, 3, 4, 5, and 6. The data can be obtained free of charge via htpp://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated with this article can be found, in the online version, atdoi:10.1016/j.jorganchem.2007.02.031.

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