Reaction chemistry,NMR spectroscopy,and X-ray crystallography of [Fe_2(#mu#-SiMe_2)_2 (CO)_4)] and [Fe_2(mu#-SiMeCl)_2(CO)_4].Electronic structure and bonding in Fe_2E_2 rings of [Fe_2(#mu#-ER_2)_2 (CO)_4] binuclear complexes (E=C,Si,Ge,Sn,Pb)

摘要

The rings [Fe_2(3mu#-Sirr')_2(CO)_8] (R=Me,R'=Me or Cl) react with HMPA togive the base-stabilized silylenes [Fe(-SiRR'(HMPA)(CO)_4].The reactions of [Fe_2(#mu#-SiMe_2)_2 (CO)_8] with DABCO,THF and PMe_3 have also been examined.The crystalstructures of both[Fe_2(#mu#-SiMe_2)_2(CO)_8] and Fe_2(#mu#-SiMeCl)_2(CO)_8] show planar rings,C-H…Oident toC short contacts and realtively short but non-bonding Si-Si distances.The possiblility of through-ring M-M or E-E bonding in complexes of the type [M_2(#mu#-ER_2)_2(CO)_8] (M is a transition metal and E is a Group 14 element) is analyzed withthe help of the oretical calculations based on density functional theory.For compounds with 20 ring electrons (or a framework electron count,FEC,of eight),regular M_2E_2 rings are expected,with no short through-ring distances.The framework electron counting rules,geometry optimization of several model complexes and a structurql fatabase analysis consistently indicate that through-ring bonding exists only when the FEC is less than eight.In that case,the isomer with a short metal-metal bond is found to be significantly more stable than that with a short E-E distance.