Reactivity of Cationic Agostic and Carbene Structures Derived from Platinum(II) Metallacycles

Abstract

This paper describes the formation of new platinacyclic complexes derived from the phosphine ligands PiPr2Xyl, PMeXyl2, and PMe2Ar Xyl 2 (Xyl=2,6‐Me2C6H3 and Ar Xyl 2=2,6‐(2,6‐Me2C6H3)2‐C6H3) as well as reactivity studies of the trans‐[Pt(C^P)2] bis‐metallacyclic complex 1 a derived from PiPr2Xyl. Protonation of compound 1 a with [H(OEt2)2][BArF] (BArF=B[3,5‐(CF3)2C6H3]4) forms a cationic δ‐agostic structure 4 a, whereas α‐hydride abstraction employing [Ph3C][PF6] produces a cationic platinum carbene trans‐[Pt{PiPr2(2,6‐CH(Me)C6H3}{PiPr2(2,6‐CH2(Me)C6H3}][PF6] (8). Compounds 4 a and 8 react with H2 to yield the same 1:3 equilibrium mixture of 4 a and trans‐[PtH(PiPr2Xyl)2][BArF] (6), in which one of the phosphine ligands participates in a δ‐agostic interaction. DFT calculations reveal that H2 activation by 8 occurs at the highly electrophilic alkylidene terminus with no participation of the metal. The two compounds 4 a and 8 experience C–C coupling reactions of a different nature. Thus, 4 a gives rise to complex trans‐[PtH{(E)‐1,2‐bis(2‐(PiPr2)‐3‐MeC6H3)CHCH}] (7) that contains a tridentate diphosphine–alkene ligand, through agostic CH oxidative cleavage and C–C reductive coupling steps, whereas the C–C coupling reaction in 8 involves classical migratory insertion of its [PtCH] and [PtCH2] bonds promoted by platinum coordination of CO or CNXyl. The mechanisms of the CC bond‐forming reactions have also been investigated by computational methods.

Synthesis, Structure and Nickel Carbonyl Complexes of Dialkylterphenyl Phosphines

“…[23][24][25] Our first reports centred on Rh, Ir,P ta nd Au complexes of PMe 2 Ar' phosphines (Ar' = C 6 H 3 -2,6-(C 6 H 3 -2,6-R 2 ) 2 forR = Me and iPr,i ns horthand notation PMe 2 Ar Xyl 2 and PMe 2 Ar Dipp 2 ,r espectively), and evinced their aptitude to stabilize low-coordinate structures, as well as their potentialt oadopt different coordination modes (Figure 1), where P-bondingi sc omplement-ed by relativelyw eak M···C arene interactions with af lanking aryl ring of the terphenyl substituent. [23][24][25][26][27][28] The objective of the present work was the description of a series of PR 2 Ar' molecules selected in accordance with the following criteria. Firstly,b esides someP Me 2 -containing phosphines, [28,29] we set out to prepare PR 2 Ar' phosphines of the branched andc yclic alkyl groups iPr and c-C 6 H 11, respectively, which are phosphine substituents extensively employed in organometallic chemistry and catalysis.…”

“…Differentc oordination modes found for terphenyl phosphines. [23][24][25][26][27][28] analogous phosphine dicarbonyl Ni 0 compounds are unknown. Furthermore, we were surprised to learn that nearly fifty years after the generation by To lman of Ni(CO) 3 (PR 3 )c omplexes in CH 2 Cl 2 solutions, [35] there is an astonishing dearth of crystallographic information on compounds of this type.…”

Synthesis and Structures of Stable PtII and PtIV Alkylidenes: Evidence for π‐Bonding and Relativistic Stabilization

“…The behavior of cationic alkylidene 2 Pt towards nucleophiles was probed by reaction with ethyldiazoacetate, 4‐dimethylamino pyridine (DMAP) or hydrogen to observe analogous reactivity to Carmona's metallocyclic carbene complex II . All reactions failed to give well‐defined, isolable products (Scheme ).…”

Non-heteroatom-substituted alkylidene complexes of groups 10 and 11

“…Our reports of 2012 and 2015 on the characterization and reactivity of a cationic platinum(II) alkylidene are to the best of our knowledge the first documented studies on a well-defined platinum species of this type. 30,48 The coordination environment of the metal centre had to be accurately designed to prevent the facile decomposition of the incipient, highly reactive carbene. The bis-platinacyles shown in Scheme 20, based on the bulky phosphines P i Pr2Xyl and PMeXyl2, were treated with a trityl salt in order to remove a hydride from the Pt-CH2 unit and form a cationic alkylidene complex.…”