Cleavage of Ge–Ge and Sn–Sn Triple Bonds in Heavy Group 14 Element Alkyne Analogues (EAr^iPr₄)₂ (E = Ge, Sn; Ar^iPr₄ = C₆H₃-2,6(C₆H₃-2,6-ⁱPr₂)₂) by Reaction with Group 6 Carbonyls

Abstract

The reactions of heavier group 14 element alkyne analogues (EAr iPr 4 ) 2 (E = Ge, Sn; Ar iPr 4 = C 6 H 3 -2,6-(C 6 H 3 -2,6- i Pr 2 ) 2 ) with the group 6 transition-metal carbonyls M(CO) 6 (M = Cr, Mo, W) under UV irradiation resulted in the cleavage of the E–E triple bond and the formation of the complexes {Ar iPr 4 EM(CO) 4 } 2 ( 1 – 6 ), which were characterized by single crystal X-ray diffraction as well as by IR and multinuclear NMR spectroscopy. Single-crystal X-ray structural analyses of 1 – 6 showed that the complexes have a nearly planar rhomboid M 2 E 2 core with three-coordinate group 14 atoms. The coordination geometry at the group 6 metals is distorted octahedral formed by four carbonyl groups as well as two bridging EAr iPr 4 units. IR spectroscopic data suggest that the EAr iPr 4 units are not very efficient π-acceptors, but the investigation of E–M metal–metal interactions in 1 – 6 with computational methods revealed the importance of both σ- and π-type contributions to bonding. The mechanism for the insertion of transition-metal carbonyls into E–E bonds in (EAr iPr 4 ) 2 was also probed computationally.