Preparation of trimethylsilyl alkyne complexes of bis(pentamethylcyclopentadienyl)zirconium, ( η5-C 5Me 5) 2Zr(RC≡CSiMe 3), and their regioselective reactions with nitrous oxide

Abstract

Benzene solutions of Cp * 2ZrCl 2 ( 1) (Cp * = η 5-C 5Me 5) react with the alkynes Me 3SiC≡CPh, Me 3SiC≡C( c-C 5H 9) and Me 3SiC≡CCMe 3 in the presence of Na/Hg amalgam to afford high yields of the respective alkyne complexes Cp * 2Zr(Me 3SiC≡CPh) ( 2), Cp * 2Zr{Me 3SiC≡C( c-C 5H 9)} ( 3) and Cp * 2Zr(Me 3SiC≡CCMe 3) ( 4) as crystalline compounds. Complex 2 crystallizes in the triclinic space group P 1 ¯ with a = 9.791(6), b = 10.466(6), c = 15.756(12) Å, α = 86.09 (5), β = 72.09(5), γ = 72.06(4)° and Z = 2. The least-squares refinement converged to R(F) = 0.0604 and R(wF) = 0.0628 for the 3655 unique data with F o > 4 σ ( F o). Salient metrical parameters of the bound alkyne include the following: C(30)-C(31) = 1.340(9) Å; Zr-C(30) = 2.178(6) Å; Zr-C(31) = 2.219(5) Å; C(30)-C(31)-Si = 141.0(5)°; C(31)-C(30)-C(26) = 135.5(5)°. Nitrous oxide reacts with 2 or 3 to afford C p * 2 Z r ( O C R = ⎴ C S i M e 3 ) (( 5) R = Ph; ( 6) R = c-C 5H 9) and 1 equiv. of N 2 via an intermediate, C p * 2 Z r { N ( O ) N C R = ⎴ C S i M e 3 } , which is unstable with respect to loss of dinitrogen to give the oxametallacyclobutene derivatives 5 and 6. The oxygen-atom insertion is regiospecific for the Zr-C bond that is attached to the carbyl (Ph or c-C 5H 9) substituent. Under similar conditions, complex 4, in which the alkyne is particularly labile, gives a myriad of products in its reaction with N 2O.