Cationic Methyl(hydrido)platinum(IV) Complexes

Abstract

The new complex [PtMe2(BPMA)], 1, BPMA = bis(2-pyridylmethyl)amine, is shown to contain bidentate BPMA with one of the pyridyl groups not coordinated to platinum. Complex 1 reacts with HX (X = Cl, BF4) at room temperature to yield [PtHMe2(BPMA)][X], which may exist in two isomeric forms, each containing tridentate BPMA. The major initial product 2 has the hydride trans to a pyridyl group, but this equilibrates with isomer 3 in which the hydride is trans to an amine. The cationic methyl(hydrido)platinum(IV) complexes 2 and 3 are stable at room temperature for several hours, but undergo slow reductive elimination of CH4 to yield [PtMe(BPMA)][X], 4. Complex 1 reacts with DCl to give [PtDMe2(BPMA)][X], and deuterium incorporation at the methyl group trans to amine occurs slowly; the methane formed by subsequent reductive elimination is a mixture of CH4, CH3D, and CH2D2. Reaction of 1 with MeI initially yields a mixture of two compounds, [PtMe3(BPMA)][I], 5a, and a neutral compound, [PtIMe3(BPMA)], 6, but 6 isomerizes to 5 over a period of 2 h at room temperature. Reaction of 1 with CD3I gives [PtMe2(CD3)(BPMA)][I], 5a *, and [PtIMe2(CD3)(BPMA)], 6 *, with CD3 largely trans to pyridyl or iodide, respectively, but equilibration gives a mixture of 5a * and 5a **, in which CD3 is trans to amine. In contrast to the reaction with MeI, oxidative addition of CF3SO3Me to 1 gives only [PtMe3(BPMA)][CF3SO3], 5b. Reaction of 1 with allyl bromide yields a mixture of two products, [PtMe2(CH2CHCH2)(BPMA)][Br], 7, and [PtBrMe2(CH2CHCH2)(BPMA)], 8; complex 8 isomerizes rapidly to 7. Complexes 4 and 7 have been characterized by X-ray structure determinations and are shown to contain the BPMA ligands in fac and mer coordination modes.

Homogeneous Oxidation of Alkanes by Electrophilic Late Transition Metals

“…Furthermore, in deuterated acidic media, multiple H/ D exchange into the alkyl positions is observed prior to elimination of the alkane for certain classes of these alkyl hydride complexes. [56,60,61,66] The results from these studies support the mechanism shown in Scheme 5 for the protonolysis of alkylplatinum(ii) complexes: a) chloride-or solventmediated protonation of Pt II (F) to generate an alkyl(hydrido)platinum(iv) intermediate (G); b) dissociation of the solvent molecule or chloride to generate a cationic, fivecoordinate platinum(iv) species (H); c) reductive C ± H Scheme 5. Proposed mechanism for the protonolysis of alkylplatinum(ii) complexes, the microscopic reverse of C ± H activation by Pt 2À is present in the reaction mixture, ethyl chloride is generated.…”

Combined Low Temperature Rapid Scan and1H NMR Mechanistic Study of the Protonation and Subsequent Benzene Elimination from a (Diimine)platinum(II) Diphenyl Complex Relevant to Arene C−H Activation

“…66,67 Other studies also observed hydridoalkylplatinum(IV) species during low-temperature protonation. [68][69][70][71][72] This lead to the assumption of an oxidative addition mechanism of an alkane to the metal, presumably from a 75 With bulky substituent in the ortho position of the diimine ligand, η 2 -benzene coordination appeared rate limiting while in the absence of ortho substituent, the C-H cleavage became the rate determining step. This was explained by steric destabilisation of both the intermediate π-benzene complex and the transition state by the ortho methyl group.…”

Functional ligands and complexes for new structures, homogeneous catalysts and nanomaterials

“…Its transition metal complexes display a rich chemistry and have a considerable importance in homogeneous catalysis because they often represent key intermediates in C-C coupling reactions [22]. Whereas the g 3 bonding mode is the most general for this ligand, some g 1 -allyl complexes have been isolated, mainly with platinum [23], rhodium [24], iridium [25], or early transition metals [26]. This g 1 -allyl type of bonding to a transition metal affects the stereochemistry of reactions proceeding via allyl intermediates and it is well known in Pd-allyl chemistry that a g 3 -g 1 -g 3 dynamic behaviour may be operative which can be either detrimental to, or required for enantioselection [22].…”