Synthesis and structure of silylene complexes of silacyclobutanes

Reactions of 1.1-dichloro-2-neopentyl-3-vinyl-l-silacyclobutane (1a, b) with carbonyl metallates [{M(CO)_n}_m]^2- (M = Fe, m = 1, n = 4; M = Cr, m = 1, n = 5; M = W, m = 2, n = 5) in THF/HMPA lead to novel compounds [(CO)_nMSiC₁₀H₁₈] · HMPA (M = Fe, n = 4; M = Cr, W, n = 5). ¹H, ¹³C and ²⁹Si NMR spectroscopic studies in solution support the formation of four diastereomeric pairs of enantiomers. The X-ray structure analyses of the crystals show folded 1-metallated 1-silacyclobutane units in which the HMPA ligand increases the coordination number of Si to 3 + 1. Crystals of [(CO)₅CrSiC₁₀H₁₈] · HMPA (2) and of [(CO)₅WSiC₁₀H₁₈] · HMPA (3) (corresponding values in brackets) are isotypic: P2₁/n (No. 14); a = 1084(1)/[1099(1)], b= 1927(1)/[1937(1)], c= 1342.1(8)/[1342(1)] pm, β = 97.11(7)/[97.18(7)]°, Z = 4. In both crystals enantiomeric [1S,2S,3S]/[1R,2R,3R] pairs are present. In orthorhombic crystals of [(CO)₄FeSiC₁₀H₁₈]. · HMPA (4) (P2₁2₁2₁ (No. 19), a = 896.4(5), b = 1693(1), c = 1753(1) pm, Z= 4) only the [1S,2S,3S]-isomer is detected.