Pincer “Hemilabile” Effect. PCN Platinum(II) Complexes with Different Amine “Arm Length”

The reactivity of the “long arm” PCN-type pincer ligand C6H4[CH2P(tBu)2](CH2)2N(CH3)2 (1), which forms complexes bearing a six-membered amine chelate and a five-membered phosphine chelate, was compared with that of the new “normal” PCN ligand C6H4[CH2P(tBu)2](CH2)N(CH2CH3)2 (2), which leads to formation of complexes bearing two five-membered chelates. The chloride complexes (PCN)PtCl (3, 4) and the unsaturated cationic complexes [(PCN)Pt]+X- (X = BF4, OTf) (5, 6, 7), based on both PCN ligands, were prepared and reacted with different reagents to give aqua, [(PCN-1)Pt(H2O)]+BF4 - (10); hydroxo, (PCN-1)Pt(OH) (11); carbonyl [(PCN)Pt(CO)]+BF4 - (8, 9); and hydride, (PCN-1)PtH (16) complexes. The structures of complexes 4, 6, 8, 10, 11, and 12 were determined by X-ray crystallography. When both carbonyl complexes were treated with hydrogen gas, the “long arm” PCN-1-based complex 8 led to formation of a trimeric cluster, [C6H6[CH2P(tBu)2](CH2)2N(CH3)2Pt(CO)]3 (12), while the “normal” PCN-based complex 9 remained unchanged under the same conditions. This observation clearly demonstrates the very significant effect of the amine arm length (five- vs six-membered chelate) on the hemilability of the ligand and the reactivity of the corresponding complexes.