Synthesis and coordination chemistry of neutral phospha(III)guanidines. Formation of 1-aza-3-phospha-4-metallacyclobut-1-ene rings at group 6 metals

The neutral phospha(III)guanidine compounds, Ph2PC{NR} {NHR} (1a, R = Cy; 1b, R = iPr), are reported. NMR spectroscopic data indicated the presence of the Esyn isomer in solution and structural studies confirmed this in the solid-state. Reaction of 1a with M(CO) 4(pip)2 [M = Mo, W; pip = piperidine] proceeded via displacement of the piperidine ligands to generate the complexes M[Ph 2PC{NCy} {NHCy}](CO)4 (2a, M = Mo; 3a, M = W). The X-ray structure of 2a and 3a were solved, showing the first structurally characterised examples of 1-aza-3-phospha-4-metallacyclobut-1-ene rings.