The catalytic activity difference of bis(phosphinite) pincer ligated Pt(II) thiolate and hydride complexes against hydrosilylation of aldimines

Abstract

• POCOP pincer Pt thiolate and hydride complexes are good catalysts for hydrosilylation of aldimines • The thiolate complexes are more active than the hydride complexes • The reactions feature with good functional group compatibility and wide substrate scope • The expected amine products can be isolated in good to excellent yields In order to get information about the catalytic activities of bis(phosphinite) (POCOP) pincer ligated group 10 metal thiolate and hydride complexes against the hydrosilylation of unsaturated carbon-heteroatom bonds, platinum(II) complexes [2,6-( t Bu 2 PO) 2 C 6 H 3 ]PtX (X = SH, 1a; SPh, 1b; H, 1c) and [2,6-( i Pr 2 PO) 2 C 6 H 3 ]PtH (2) were applied to the catalytic hydrosilylation of aldimines. It was found that both auxiliary ligand and donor substituent play very important roles in affecting the catalytic activity of the platinum center. The hydride complex 1c is almost inactive in catalyzing the reactions; however, the hydride complex 2, which processes less bulky donor substituents ( i Pr vs t Bu), is an active catalyst. Meanwhile, the thiolate complexes 1a and 1b, which have the same donor substituents as 1c, are active catalysts and 1a is among most effective catalysts for this type of reaction. The catalytic reactions are featured with a wide substrate scope with relatively high turnover frequencies. Both aromatic and aliphatic aldimines were successfully hydrosilylated and the expected amines were isolated in good to excellent yields after basic hydrolysis of the hydrosilylation products. Functional groups such as OMe, halogens and internal C=C double bond were unaffected during the reactions. Although the hydride complex 2 is an active catalyst, it is less effective than the thiolate complex 1a despite the fact that the metal center in 2 is less sterically hindered by the donor substituents. As a result, the thiolate complexes are more active than the hydride complexes in catalyzing the reactions. The possible reasons for the different catalytic activities of these complexes are discussed.