P,N-Chelate Complexes of Pd(II) and Pt(II) Based on a Phosphaalkene Motif: A Catalyst for the Overman−Claisen Rearrangement

Abstract

The reaction of E/Z-MesPC(Ph)(Py) (1, Mes = 2,4,6-Me3C6H2-) with (cod)PtCl2 or (cod)PdCl2 affords P,N-chelate complexes [MesPC(Ph)(Py)PtCl2] (2a) and [MesPC(Ph)(Py)PdCl2] (2b), respectively. Compounds 2a and 2b were fully characterized spectroscopically, and both were characterized by X-ray crystallography. The molecular structures exhibited almost identical metrical parameters. The PC bond lengths in 2a and 2b [1.672(4) and 1.675(3) Å, respectively] were shortened substantially with respect to that of 1 [1.7043(16) Å]. Complex 2b was explored as a catalyst for the Overman−Claisen rearrangement. Several allyl trichloroacetimidate substrates [HNC(CCl3)OCH2CHCHR1: 3a, R1 = Me; 3b, R1 = n-Pr; 3c, R1 = n-Hep; 3d, R1 = CH2CH2Ph; 3e, R1 = i-Pr] were successfully rearranged to their respective branched amides [H2CCHCH(R1)NHC(O)CCl3: 4a−e] using 5 mol % 2b as catalyst. Isolated yields ranged from a low of 33% for the bulky 4e to a high of 91% for 4a.