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

The reactivity of the “long arm” PCN-type pincer ligand C 6 H 4 [CH 2 P(tBu) 2 ](CH 2 ) 2 N(CH 3 ) 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 C 6 H 4 [CH 2 P(tBu) 2 ](CH 2 )N(CH 2 CH 3 ) 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 = BF 4, OTf) ( 5, 6, 7 ), based on both PCN ligands, were prepared and reacted with different reagents to give aqua, [(PCN- 1 )Pt(H 2 O)] + BF 4 - ( 10 ); hydroxo, (PCN- 1 )Pt(OH) ( 11 ); carbonyl [(PCN)Pt(CO)] + BF 4 - ( 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, [C 6 H 6 [CH 2 P(tBu) 2 ](CH 2 ) 2 N(CH 3 ) 2 Pt(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.