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

• Synthesis of novel [(CO)4(PPh3)M(OEt)(aryl)-carbene] complexes, M = Cr or Mo.
• First crystal structure of a trans-[(CO)4(PPh3)M-carbene], M = W.
• Crystal structures of cis-[(CO)4(PPh3)M-carbene] complexes.
• PPh3 orientation in octahedral trans- and cis-[(CO)4(PPh3)M-carbene] complexes.
• Remarkable performance of DFT to determine PPh3 orientation.

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.

Orientation of triphenylphosphine in octahedral [(CO)4(PPh3)W-carbene] complexes.Figure optionsDownload as PowerPoint slide