True and masked three-coordinate T-shaped platinum(II) intermediates

Although four-coordinate square-planar geometries, with a formally 16-electron counting, are absolutely dominant in isolated Pt(II) complexes, three-coordinate, 14-electron Pt(II) complexes are believed to be key intermediates in a number of platinum-mediated organometallic transformations. Although very few authenticated three-coordinate Pt(II) complexes have been characterized, a much larger number of complexes can be described as operationally three-coordinate in a kinetic sense. In these compounds, which we have called masked T-shaped complexes, the fourth position is occupied by a very weak ligand (agostic bond, solvent molecule or counteranion), which can be easily displaced. This review summarizes the structural features of the true and masked T-shaped Pt(II) complexes reported so far and describes synthetic strategies employed for their formation. Moreover, recent experimental and theoretical reports are analyzed, which suggest the involvement of such intermediates in reaction mechanisms, particularly C–H bond-activation processes

Different coordination modes of an aryl-substituted hydrotris(pyrazolyl) borate ligand in rhodium and iridium complexes

Complexes TptolRh(C2H4)2 (1a) and TptolRh(CH2C(Me)C(Me)CH2) (1b) have been prepared by reaction of KTptol with the appropriate [RhCl(olefin)2]2 dimer (Tptol means hydrotris(3-p-tolylpyrazol-1-yl)borate). The two complexes show a dynamic behaviour that involves exchange between κ2 and κ3 coordination modes of the Tptol ligand. The iridium analogue, TptolIr(CH2C(Me)CHCH2) (2) has also been synthesized, and has been converted into the Ir(III) dinitrogen complex [(κ4-N,N',N'',C-Tptol)Ir(Ph)(N2) (3) by irradiation with UV light under a dinitrogen atmosphere. Compound 3 constitutes a rare example of Ir(III)-N2 complex structurally characterized by X-ray crystallography. Its N2 ligand can be easily substituted by acetonitrile or ethylene upon heating and denticity changes in the Tptol ligand, from κ4-N,N',N'',C (monometallated Tptol, from now on represented as Tptol′) to κ5-N,N′,N″,C,C″ (dimetallated Tp tol ligand, represented as Tptol″) have been observed. When complex 3 is heated in the presence of acetylene, dimerization of the alkyne takes place to yield the enyne complex [(κ5-N,N′,N′′,C,C′-Tp tol)Ir(CH2CHCCH), 7̧ in which the unsaturated organic moiety is bonded to iridium through the carbon-carbon double bond.Ministerio de Educación y Ciencia CTQ2007-62814Consolider-Ingenio 2010 CSD2007-00006Junta de Andalucía FQM-3151, FQM-672CONACYT 22934

Synthesis, properties, and some rhodium, iridium, and platinum complexes of a series of bulky m-terphenylphosphine ligands

A series of sterically demanding aryl phosphine ligands (L) bearing terphenyl substituents, PR2Ar′ (R = hydrocarbyl, Ar′ = 2,6-diarylphenyl radical) has been prepared and characterized. The stability of these ligands towards oxidation in the air has been tested, and theoretical and experimental studies aimed to provide information on their electronic and steric properties have been performed. Treatment of the metal dimers [MCl(COD)]2(M = Rh, Ir; COD = 1,5-cyclooctadiene) with ligands PMe2ArXyl2(L1) and PMe2ArDipp2(L5), in a 1:1 metal:ligand ratio, afforded the expected square-planar 16-electron complexes [MCl(COD)(PMe2ArXyl2)] and [MCl(COD)(PMe2ArDipp2)], respectively. These compounds were readily converted into the corresponding dicarbonyl derivatives, [MCl(CO)2(PMe2ArXyl2)] and [MCl(CO)2(PMe2ArDipp2)], respectively. While the expected κ1-P coordination mode of the PR2Ar′ ligands is found for these rhodium and iridium species, the mononuclear Pt(II) derivative obtained by reaction of PtCl2with PMe2ArDipp2has composition [PtCl2(PMe2ArDipp2)], and exhibits a bidentate κ1-P, η1-arene coordination mode involving one of the ipso carbon atoms of a flanking terphenyl aryl ring. The corresponding carbonyl compound [PtCl2(CO)(PMe2ArDipp2)], was generated under a CO atmosphere and exhibits κ1-P coordination mode.Ministerio de Ciencia CTQ2013-42501-P, CTQ2014-51912-REDC, CTQ-2014-52769-C3-3-RJunta de Andalucía FQM-119 P09-FQM-4832, FQM-2126European Union 26722

Isolation of a Cationic Platinum(II) s-Silane Complex

The platinum complex [Pt(ItBuiPr¿)(ItBuiPr)][BArF] interacts with tertiary silanes to form stable (<0 C) mononuclear PtII sigma-SiH complexes [Pt(ItBuiPr¿)(ItBuiPr)(eta1-HSiR3)][BArF]. These compounds have been fully characterized, including X-ray diffraction methods, as the first examples for platinum. DFT calculations (including electronic topological analysis) support the interpretation of the coordination as an unusual eta1-SiH. However, the energies required for achieving a eta2-SiH mode are rather low, and is consistent with the propensity of these derivatives to undergo Si-H cleavage leading to the more stable silyl species [Pt(SiR3)(ItBuiPr)2]- [BArF] at room temperature.Peer Reviewe