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

Abstract

The synthesis and selected crystal structures of novel (M=Cr or Mo) and known (M=W) [(CO)4(PPh3)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 (PPh3) in octahedral [(CO)4(PPh3)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 PPh3 involves a correlated feathering of the phenyl groups with the PCipso bond of one phenyl group orientated near parallel to the nadir plane, and a meta carbon (Cm) of the other two phenyl groups orientated as near as possible to the nadir plane, orthogonal to the first. Although the orientation of PPh3 in 6-trans, [(CO)4(PPh3)W=C(OEt)2-furyl], deviates from this, DFT correctly calculated the unexpected and not generally observed PPh3 orientation.