Reactivities of a Bis(alkylidene) Complex. Synthesis of a Silyl Bis(alkylidyne) Complex and a Reaction Cycle among Symmetric Bis(alkylidyne), Bis(alkylidene), and Nonsymmetric Bis(alkylidyne) Compound
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- 作者：Xiaozhan Liu ; Liting Li ; Jonathan B. Diminnie ; Glenn P. A. Yap ; Arnold L. Rheingold ; and Ziling Xue
- 刊名：Organometallics
- 出版年：1998
- 出版时间：October 12, 1998
- 年：1998
- 卷：17
- 期：21
- 页码：4597 - 4606
- 全文大小：249K
- 年卷期：v.17,no.21(October 12, 1998)
- ISSN：1520-6041
文摘
An unstable bis(alkylidene) complex (RCH2)4Ta2(=CHR)2(Cl)2 (R = SiMe3, 1), preparedby the addition of 2 equiv of HCl to a symmetrically bridging bis(alkylidyne) complex (RCH2)4Ta2(
-CR)2 (2a), decomposes through elimination of SiMe4 to form an unstable alkylidene-alkylidyne complex (RCH2)3Ta2(=CHR)(
CR)(Cl)2 (3). This conversion of an alkylidene toalkylidyne ligand was found to follow first-order kinetics with 
H1
= 14.1(0.8) kcal/moland S1 = -12(3) eu. This is, to our knowledge, the second reported kinetic study ofalkylidene 
alkylidyne conversion, and the kinetics of this conversion is in contrast to thatof (RCH2)3Ta=CHR (RCH2)4Ta2(-CR)2 (2a) reported earlier. Substitution of the chloridesby SiR3- (R = SiMe3) leads to a preferential elimination of HSiR3 and formation of the firstsilyl bis(alkylidyne) complex (RCH2)(R3Si)Ta(-CR)2Ta(CH2R)2 (4). Addition of excess PMe3to 1 produces a novel 1,1'-dimetallacyclobutadiene derivative (Me3P)2(Cl)Ta(-CR)2Ta(Cl)(CH2R)2 (5a) with two nonsymmetrically bridging alkylidyne ligands. Both bridging ligandscoordinate with C=Ta double bonds to the same metal atom (and with C-Ta single bondsto the other metal atom). The two bridging alkylidyne ligands in 5a, which are coordinatedto one metal atom in the axial and equatorial position, respectively, are involved in anintramolecular ligand exchange. The kinetic barriers for this exchange were determined tobe H2 = 13.6(0.4) kcal/mol and S2 = -5(2) eu in 5a, and H3 = 13.0(0.3) kcal/mol andS3 = -5(1) eu in 5b. Addition of 2 equiv of RCH2Li to replace the Cl ligands in 5a converts5a to 2a, completing a reaction cycle 2a 1 5a 2a. (Me3P)2(RCH2)Ta(-CR)2Ta(Cl)(CH2R)2 (6) was identified as an intermediate in the conversion of 5a to 2a.
-CR)2 (2a), decomposes through elimination of SiMe4 to form an unstable alkylidene-alkylidyne complex (RCH2)3Ta2(=CHR)(CR)(Cl)2 (3). This conversion of an alkylidene toalkylidyne ligand was found to follow first-order kinetics with H1 = 14.1(0.8) kcal/moland S1 = -12(3) eu. This is, to our knowledge, the second reported kinetic study ofalkylidene alkylidyne conversion, and the kinetics of this conversion is in contrast to thatof (RCH2)3Ta=CHR (RCH2)4Ta2(-CR)2 (2a) reported earlier. Substitution of the chloridesby SiR3- (R = SiMe3) leads to a preferential elimination of HSiR3 and formation of the firstsilyl bis(alkylidyne) complex (RCH2)(R3Si)Ta(-CR)2Ta(CH2R)2 (4). Addition of excess PMe3to 1 produces a novel 1,1'-dimetallacyclobutadiene derivative (Me3P)2(Cl)Ta(-CR)2Ta(Cl)(CH2R)2 (5a) with two nonsymmetrically bridging alkylidyne ligands. Both bridging ligandscoordinate with C=Ta double bonds to the same metal atom (and with C-Ta single bondsto the other metal atom). The two bridging alkylidyne ligands in 5a, which are coordinatedto one metal atom in the axial and equatorial position, respectively, are involved in anintramolecular ligand exchange. The kinetic barriers for this exchange were determined tobe H2 = 13.6(0.4) kcal/mol and S2 = -5(2) eu in 5a, and H3 = 13.0(0.3) kcal/mol andS3 = -5(1) eu in 5b. Addition of 2 equiv of RCH2Li to replace the Cl ligands in 5a converts5a to 2a, completing a reaction cycle 2a 1 5a 2a. (Me3P)2(RCH2)Ta(-CR)2Ta(Cl)(CH2R)2 (6) was identified as an intermediate in the conversion of 5a to 2a.