The mechanisms of fluxionality of [Fe3(CO)12 –n{P(OR)3}n](R = Me, n= 0–3; R = Pri, n= 2 or 3) and the X-ray structure of [Fe3(CO)10{P(OMe)3}2]

Abstract

The solution structures of the major isomers of [Fe₃(CO)₁₀{P(OMe)₃}₂] and [Fe₃(CO)₉{P(OMe)₃}₃] have been unambiguously established in solution. Probable structures of [Fe₃(CO)₁₁{P(OMe)₃}], the minor isomers of [Fe₃(CO)₁₀{P(OMe)₃}₂] and [Fe₃(CO)₉{P(OMe)₃}₃], and the major isomer of [Fe₃(CO)₉{P(OPrⁱ)₃}₃] in solution are proposed. The solution structures of [Fe₃(CO)₁₂] and [Fe₃(CO)₁₁{P(OMe)₃}] are discussed. It is shown that there is a very-low-energy dynamic process which is apparent in the carbonyl positions of the crystal structure of [Fe₃(CO)₁₂]. In addition, there are three, and probably four, higher-energy dynamic processes which have been established from ¹³C and ³¹P n.m.r. investigations. The implications of the low-energy dynamic process in the solid-state ¹³C n.m.r. spectrum are discussed. The X-ray structure of [Fe₃(CO)₁₀{P(OMe)₃}₂] shows it to have the P(OMe)₃ ligands forming an approximately linear P–Fe–Fe–P arrangement, with bridging carbonyls between the unique unsubstituted iron and a substituted iron. Disorder prevented an accurate structure determination.