Conformation analysis of triphenylphosphine in trans and cis triphenylphosphine-substituted Fischer carbene complexes

The synthesis and selected crystal structures of novel (M = Cr or Mo) and known (M = W) [(CO) 4 (PPh 3 )M = C(OEt)R] complexes, M = Cr, R = 2-thienyl ( 1 ), 2-furyl ( 2 ); M = Mo, R = 2-thienyl ( 3 ), 2-furyl ( 4 ); M = W, R = 2-thienyl ( 5 ), 2-furyl ( 6 ), are presented. Experimental crystal structures and DFT calculations of selected trans- and cis- triphenylphosphine-substituted Fischer carbene complexes, illustrate that the minimum energy conformation of triphenylphosphine (PPh 3 ) in octahedral [(CO) 4 (PPh 3 )ML]-complexes generally have distinct features that can be described in terms of the “ plane of nadir energy ”, a plane linking all points of minimum steric compression between the ligands. The generally observed orientation of PPh 3 involves a correlated feathering of the phenyl groups with the P C ipso bond of one phenyl group orientated near parallel to the nadir plane, and a meta carbon (C m ) of the other two phenyl groups orientated as near as possible to the nadir plane, orthogonal to the first. Although the orientation of PPh 3 in 6 - trans , [(CO) 4 (PPh 3 )W = C(OEt)2-furyl], deviates from this, DFT correctly calculated the unexpected and not generally observed PPh 3 orientation.