Hemilability of P(X)N-type ligands (X = O, N–H): rollover cyclometalation and benzene C–H activation from (P(X)N)PtMe₂complexes

Abstract

The thermolyses of ((tBu)P(O)N)PtMe2 (, (tBu)P(O)N = (di-tert-butylphosphinito)pyridine) and ((tBu)P(N-H)N)PtMe2 (, (tBu)P(N-H)N = (di-tert-butylphosphino)-2-aminopyridine) in benzene-d6 were investigated. With ((tBu)P(O)N)PtMe2, the product of a rollover cyclometalation of the pyridyl ring was observed in 80% yield along with formation of CH4. In contrast, thermolysis of ((tBu)P(N-H)N)PtMe2 resulted in competing rollover cyclometalation and intermolecular benzene C-H activation with production of a mixture of CH4 and CH3D.

Methoxycarbonylation of Styrene Using a New Type of Palladium Complexes Bearing P,N-donor Ligands as Catalysts

“…Remarkably, the complex with the pyrimidine ligand [PdCl(Ph 2 PNHpym)(PPh 3 )]Cl, generated in situ by reaction between the neutral complex and PPh 3 , achieves practically complete conversion and chemoselectivity and 97 % regioselectivity in the branched ester (entry 3), as it happens with its pyridine analog [23]. This comparable result with the pyridine ligand indicates that the reported rollover cyclometalation of the aromatic ring in related complexes [24], which is prevented in the pyrimidine ligand, does not have a contribution to the noteworthy performance of the catalysts [PdCl(P,X) (PPh 3 In summary, these catalytic experiments confirm that [PdCl(Ph 2 PNHpy)(PPh 3 )]Cl and its pyrimidine analog here described are particularly appropriate catalysts for an efficient and selective methoxycarbonylation of styrene.…”

“…A recent report revealed that the complex [Pt( t Bu 2-PNHpy)Me 2 ] undergoes partial rollover cyclometalation of the pyridyl ring concurrent with methane evolution (scheme 1) [24]. Because of the similarity of this ligand to Ph 2 PNHpy, it is not possible to exclude a priori that a metalation process also takes place during the methoxycarbonylation reaction.…”

Role of Phosphine Sterics in Strained Aminophosphine Chelate Formation

“…To address the structural properties affected by changes in the chelate size, five-membered PN chelates ( L 7 )­PtMe 2 ( 11 ; L 7 = t Bu 2 PCH 2 CH 2 NMe 2 ) and ( L 8 )­PtMe 2 [ 12 ; L 8 = (2-pyridyl)­CH 2 P t Bu 2 ] were prepared by the addition of the appropriate ligand to [Pt 2 Me 4 (μ-SMe 2 ) 2 ]. The X-ray structure of 11 was obtained and is presented for comparison with four-membered chelates in Scheme c, while the structure of 12 was reported previously by Goldberg and co-workers . The data for the four-membered chelate complexes confirm their monomeric nature and show distorted square-planar geometries (τ 4 = 0.13–0.15) because of the small ligand bite angles of close to 70° [ 7 , 71.4(2)°; 9 , 70.0(2)°; 10 , 68.90(7)°].…”

“…The X-ray structure of 11 was obtained and is presented for comparison with four-membered chelates in Scheme 3c, while the structure of 12 was reported previously by Goldberg and co-workers. 14 The data for the fourmembered chelate complexes confirm their monomeric nature and show distorted square-planar geometries (τ 4 = 0.13−0.15) 15 because of the small ligand bite angles of close to 70° [7, 71.4(2)°; 9, 70.0(2)°; 10, 68.90(7)°]. These angles are significantly smaller than those in related diphosphinomethane complexes (∼74°).…”

Rollover Cyclopalladation via Remote C‐H Bond Activation of Br‐Pyridinbenzothiazole: An Experimental Study

“…Goldberg et al. reported that thermolysis of dimethyl‐platinum complex supported by phosphinito‐pyridine and phosphino‐aminopyridine ligands in C 6 D 6 , gives cleanly the expected rollover complexes, respectively (Scheme , c) …”