Direct observation of C-O reductive elimination from palladium aryl alkoxide complexes to form aryl ethers

Reaction of KOCH2CMe3 with [(R)-Tol-BINAP]Pd(p-C6H4CN)Br formed [(R)-Tol-BINAP]Pd(p-C6H4CN)(OCH2CMe3) (5) in quantitative yield (H-1 NMR spectroscopy). Thermolysis of 5 in THF-d(8) at 47 degrees C led to C-O reductive elimination with formation of p-neopentoxybenzonitrile (85 +/- 2%). A secondary P-C bond-cleavage process led to formation of 4,4'-dimethylbiphenyl (16 +/- 2%). Kinetic analysis of the decomposition of 5 at 47 OC in the presence of excess potassium neopentoxide established the two-term rate law, rate = k[5] + k'[5][KOCH2-CMe3], where k = 1.50+/-0.07 x 10(-3) s(-1) and k'=6.2+/-0.4 x 10(-3) s(-1) M-1, consistent with reductive elimination via competing alkoxide-dependent and alkoxide-independent pathways. In addition, excess KOCH2CMe3 exchanged rapidly with the palladium-bound alkoxide ligand of 5 at 47 OC according to the rate law: rate exchange k(ex)[5][KOCH2CMe3], where k(ex) = 1.0+/-0.1 x 10(2) s(-1) M-1. Thermolysis of the related palladium p-cyanophenyl alkoxide complexes (P-P)Pd(p-C6H4CN)(OR) [P-P = (S)-BINAP, R = CH2CMe3; P-P=(R)-Tol-BINAP, R = CHMe2, CMe3; P-P=dppf, R=CH2CMe3, CMe3] and (dppf)Pd[o-C6H4(CH2)(2)C(Me)(2)O] led to aryl ether formation in 46-91% yield.