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Campos J.,Institute Investigaciones Quimicas IIQ | Kundu S.,University of North Carolina at Chapel Hill | Pahls D.R.,University of North Texas | Brookhart M.,University of North Carolina at Chapel Hill | And 2 more authors.
Journal of the American Chemical Society | Year: 2013

Evidence for key σ-complex intermediates in the hydrogenolysis of the iridium-methyl bond of (PONOP)Ir(H)(Me)+ (1) [PONOP = 2,6-bis(di-tert-butylphosphinito)pyridine] has been obtained. The initially formed η2-H2 complex, 2, was directly observed upon treatment of 1 with H2, and evidence for reversible formation of a σ-methane complex, 5, was obtained through deuterium scrambling from η2-D2 in 2-d2 into the methyl group of 2 prior to methane loss. This sequence of reactions was modeled by density functional theory calculations. The transition state for formation of 5 from 2 showed significant shortening of the Ir-H bond for the hydrogen being transferred; no true Ir(V) trihydride intermediate could be located. Barriers to methane loss from 2 were compared to those of 1 and the six-coordinate species (PONOP)Ir(H)(Me)(CO)+ and (PONOP)Ir(H)(Me)(Cl). © 2013 American Chemical Society. Source

Lopez-Rodriguez R.,Institute Investigaciones Quimicas IIQ | Lopez-Rodriguez R.,University of Seville | Ros A.,Institute Investigaciones Quimicas IIQ | Fernandez R.,University of Seville | Lassaletta J.M.,Institute Investigaciones Quimicas IIQ
Journal of Organic Chemistry | Year: 2012

A mild procedure for the Ir(III)-catalyzed nitrogen-directed ortho borylation of aromatic N,N-dialkylhydrazones using pinacolborane as the boron source has been developed. The methodology relies on a modified, hemilabile N,N ligand built on a 4-N,N-dimethylaminopyridine unit that provides high reactivity while maintaining exclusive ortho-selectivity. This procedure can be combined with Suzuki-Miyaura cross-couplings in a 'one-pot' fashion to afford functionalized biaryl derivatives that, upon subsequent 'one-pot', high yielding transformations, provide a convenient entry for the preparation of advanced benzonitrile intermediates for the synthesis of Sartan-type drugs. © 2012 American Chemical Society. Source

Ros A.,Institute Investigaciones Quimicas IIQ | Estepa B.,University of Seville | Bermejo A.,University of Seville | Alvarez E.,Institute Investigaciones Quimicas IIQ | And 2 more authors.
Journal of Organic Chemistry | Year: 2012

Phosphino hydrazones derived from C 2-symmetric hydrazines exhibit excellent catalytic activity and provide good enantioselectivities in the asymmetric Suzuki-Miyaura cross-coupling to axially chiral biaryls, in particular for the most challenging reactions of monocyclic, functionalized aryl bromides and triflates. X-ray analysis of preformed [Pd(P/N)Cl 2] precatalysts [(P/N) = phosphino hydrazone] revealed a strong n-π conjugation in the hydrazone moiety, identified by a high planarity degree at the pyrrolidine N(sp 3) atom, that makes rotations around N-N bonds inconsequential. The complexes are also characterized by an envelope-like conformation with the Pd atom placed at the opposite side to the 2-phenyl group on the nearest stereogenic center of the pyrrolidine group. The isolation and structural analysis of oxidative addition intermediates indicate that the configurational stability of Pd-C(Ar) bonds is dependent on the substitution pattern in the aryl bromide. © 2012 American Chemical Society. Source

Campos J.,Institute Investigaciones Quimicas IIQ | Espada M.F.,Institute Investigaciones Quimicas IIQ | Lopez-Serrano J.,Institute Investigaciones Quimicas IIQ | Carmona E.,Institute Investigaciones Quimicas IIQ
Inorganic Chemistry | Year: 2013

This work details the synthesis and structural identification of a series of complexes of the (η5-C5Me5)Ir(III) unit coordinated to cyclometalated bis(aryl)phosphine ligands, PR′(Ar) 2, for R′ = Me and Ar = 2,4,6-Me3C6H 2, 1b; 2,6-Me2-4-OMe-C6H2, 1c; 2,6-Me2-4-F-C6H2, 1d; R′ = Et, Ar = 2,6-Me2C6H3, 1e. Both chloride-and hydride-containing compounds, 2b-2e and 3b-3e, respectively, are described. Reactions of chlorides 2 with NaBArF (BArF = B(3,5-C 6H3(CF3)2)4) in the presence of CO form cationic carbonyl complexes, 4+, with ν(CO) values in the narrow interval 2030-2040 cm-1, indicating similar π-basicity of the Ir(III) center of these complexes. In the absence of CO, NaBArF forces κ4-P,C,C′,C″ coordination of the metalated arm (studied for the selected complexes 5b, 5d, and 5e), a binding mode so far encountered only when the phosphine contains two benzylic groups. A base-catalyzed intramolecular, dehydrogenative, C-C coupling reaction converts the κ4 species 5d and 5e into the corresponding hydrido phosphepine complexes 6d and 6e. Using CD3OD as the source of deuterium, the chlorides 2 undergo deuteration of their 11 benzylic positions whereas hydrides 3 experience only D incorporation into the Ir-H and Ir-CH 2 sites. Mechanistic schemes that explain this diversity have come to light thanks to experimental and theoretical DFT studies that are also reported. © 2013 American Chemical Society. Source

Campos J.,Institute Investigaciones Quimicas IIQ | Campos J.,University of Oxford | Ortega-Moreno L.,Institute Investigaciones Quimicas IIQ | Conejero S.,Institute Investigaciones Quimicas IIQ | And 4 more authors.
Chemistry - A European Journal | Year: 2015

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. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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