A pnictogen of peculiar posture

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Inorganic Chemistry

Background:

• Bridgeman et al. synthesized a rare organometallic cluster [{Cp(OC)2Mo}2PMn(CO)4] in 2001.
• The cluster features a unique T-shaped phosphorus atom within an organometallic framework.

Purpose of the Study:

• To elucidate the electronic structure and bonding in the [{Cp(OC)2Mo}2PMn(CO)4] cluster.
• To explain the origin of the T-shaped geometry of the phosphorus atom.
• To reconcile the observed bonding with established electron count rules.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Extended Hückel electronic structure calculations.

Main Results:

• The T-shaped geometry is attributed to a novel Mo-Mn-Mo three-center, two-electron bond.
• Stabilization of the planar structure is enhanced by Mo-P pi back-donation, forming a Mo-P-Mo three-center, four-electron pi bond.
• The compound's bonding characteristics are best described as a mu2-phosphinidene system.

Conclusions:

• The unusual bonding in the [{Cp(OC)2Mo}2PMn(CO)4] cluster explains its unique T-shaped phosphorus geometry.
• The delocalized bonding challenges simple application of the 18- and 8-electron rules.
• This study provides insights into the complex electronic structure of organometallic clusters.