Ligand-Enforced Switch of the Coordination Mode in Low-Valent Group 6 Carbonyl Complexes Containing Pyrimidine-Based Bisphosphines

Abstract

The reaction of M(CO)6 (M = Cr, Mo, W) with N,N′-bis(diisopropylphosphine)-N,N′-dimethylpyrimidine-4,6-diamines (PymR-iPr) bearing R = Me, Ph, tBu substituents in the 2-position was investigated. The pyrimidine-based bisphosphine ligands with R = Me, Ph reacted with M(CO)6 to yield mononuclear and homobimetallic complexes of the types [M(κ2P,N-PymMe-iPr)(CO)4] and [M(CO)4-μ2-(κ2P,N-PymPh-iPr)M(CO)4], respectively. Heterobimetallic complexes of the type [M1(CO)4-μ2-(κ2P,N-PymMe-iPr)M2(CO)4] were obtained by reacting mononuclear complexes [M1(κ2P,N-PymMe-iPr)(CO)4] with 1 equiv of the respective M2(CO)6. Replacing these substituents by a bulky tBu group led to a switch in the coordination mode of the pyrimidine ligand. In the case of chromium, the complex [Cr(κ3P,CH,P-PymtBu-iPr)(CO)3] containing an η2-Caryl–H agostic bond was selectively formed and no C–H bond cleavage took place. However, in the case of molybdenum, the reaction led to the formation of an inseparable mixture of the agostic complex [Mo(κ3P,...