Bulky pyrazole as ligands in rhodium(I) complexes. Crystal structure of chlorodicarbonyl (3-p-methoxyphenylpyrazole)rhodium(I)

A new family of complexes containing bulky pyrazoles substituted in the 3 or the 3 and 5 positions, [RhCl(L2)(HpzR′,R″)] (L2  NBD, 2CO; R′  But, Ph, p-CH3OC6H4 (An), R″  H; R′  But, Ph, R″  CH3; R′  R″  H, CH3), has been obtained. A dynamic behaviour has been observed only in complexes with the less demanding pyrazole ligands, relating with a metallotropic equilibrium when R′  R″  H, Me, or a diolefin reorientation when R′  But, Ph, An, R″  H. The X-ray crystal structure of [RhCl(CO)2(HpzAn)] has been solved, showing a molecular stacking with a RhRh separation of 3.398(3) A along the one-dimensional chain.