Synthesis and reactivity studies of cationic Ir(III) alkylidines. α-hydride abstraction reactions

The chemistry of late transition metal alkylidenes [M=CR2], where R is H a hydrocarbyl group, have attracted widespread attention although mainly with reference to complexes of metals in low oxidation state. We focus in this paper on reactions based on electrophilic attacks by Ph3C+ that allow either isolation of stable cationic Ir(III) alkylidenes, considerably more attractive than well-known Ir(I) counterparts, or the generation of very reactive variants that experience fast migratory insertion into existing Ir-C and Ir-H sigma bonds. The present studies are based on (η5-C5Me5)Ir(III) complexes that bear a cyclometalated PMeXyl2 ligand (Xyl = 2,6-Me2C6H3). The contribution of different monoanionic ligands (chloride, alkyl or hydride) to either stabilize the Ir=CR2 linkage or provide facile reactivity routes has been investigated, including the use of various deuterium isotopologues of the iridium complex precursors

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

This review aims to offer a detailed summary of the discoveries regarding non-heteroatom-substituted alkylidenes of group 10 and 11 metals that have appeared in the literature since the first isolable representative of this class was reported in 2002. Special attention is focused on synthetic and bonding aspects of well-defined species. The importance of this family of compounds in catalytic organic transformations is often mentioned and a number of references are provided. We stress, however, that it is not the main issue of this review, as this topic has received considerable attention in the current literature.Ministerio de Economía, Industria y Competitividad CTQ2016-75193-

Synthesis and reactivity of half-sandwich (η 5 -C 5 Me 5 )Ir(iii) complexes of a cyclometallated aryl phosphine ligand

Reaction of the Ir(iii) dimer [(η 5 -C 5 Me 5 )IrCl 2 ] 2 with PMeXyl 2 (Xyl = 2,6-C 6 H 3 Me 2 ), in the presence of the poorly coordinating base 2,2,6,6-tetramethyl piperidine, gives a chloride complex 1-Cl, resulting from hydrogen chloride elimination involving one of the phosphine benzylic hydrogen atoms and concomitant cyclometallation. Related compounds containing other halide or pseudohalide ligands, 1-Br, 1-Cl, 1-SCN, can be made, the latter featuring S-coordination of the ambidentate thiocyanate to the soft Ir(iii) Lewis acid centre, as suggested by IR data and demonstrated by X-ray crystallography. Hydride 2-H, and alkyl derivatives 3 (Me) and 4 (CH 2 SiMe 3 ) can also be prepared from 1-Cl and appropriate hydride and alkylating reagents. An interesting H/D exchange chemistry that occurs in the presence of CD 3 OD has been disclosed for 1-Cl, 1-Br and 2-H. For the halide derivatives, deuterium incorporation takes place into the methylene and methyl sites of their cyclometallated ligand, whereas for 2-H only the hydride and methylene (Ir-CH 2 ) protons participate in the exchange, which is strikingly accelerated by catalytic amounts of acids.Ministerio de Ciencia e Innovación CTQ2010-17476Consolider-Ingenio2010 CSD2007-0000Junta de Andalucia FQM-119, P09-FQM-483

Reactivity of a trans-[H-Mo≣Mo-H] Unit Towards Alkenes and Alkynes. Bimetallic Migratory Insertion, H-Elimination and Other Reactions

Complex [Mo2(H)2{μ-HC(NDipp)2}2(THF)2], (1·THF), reacts with C2H4 and PhCH[double bond, length as m-dash]CH2 to afford hydrido-hydrocarbyl and bis(hydrocarbyl) derivatives of the Mo[quadruple bond, length as m-dash]Mo bond. Reversible migratory insertion and β-hydrogen elimination, as well as reductive elimination and other reactions, have been uncovered. PhC[triple bond, length as m-dash]CH behaves instead as a Brönsted–Lowry acid towards the strongly basic Mo–H bonds of 1·THF.Ministerio de Economía y Competitividad CTQ2016-75193-PEuropean Research Council 75657

Electronic and structural effects of low hapticity coordination of arene rings to transition metals

A DFT computational study and a structural analysis of the coordination of arenes to transition metals in low -hapticity (η1 and η2) modes have been developed, including a pseudosymmetry analysis of the molecular orbitals and the introduction of a hapticity map that makes evident the different degrees of intermediate hapticities. Calculations on [PtIIL3(C6H6)] model complexes reveal a preference for the η2 mode, while the η1 coordination is found to be a low-energy transition state for a haptotropic shift. The attachment of the arene to a side group that is coordinated to the metal introduces geometrical constraints, which result in hapticities intermediate between one and two. Comparison of the η1 arene complexes with benzonium cations shows that in the former case the bonding to the metal involves essentially the π system of the arene, affecting only slightly the delocalized nature of the carbon-carbon bonds. This behavior is in sharp contrast with the frequently found η1 coordination of Cp that involves σ bonding and full dearomatization of the ring

Large-scale preparation and labelling reactions of deuterated silanes

A catalytic synthesis of deuterated silanes SiEt3D, SiMe2PhD and SiPh2D2 is reported that allows their facile generation in a 3–4 g scale, utilizing D2 (0.5 bar) as the hydrogen isotope source and low catalyst loadings (0.01 mol%). The catalyst precursor is the rhodium (III) complex 1, which contains a (η5‐C5Me5)Rh cation stabilized by coordination to a cyclometallated phoshine PMeXyl2 (Xyl = 2,6‐C6H3Me2). The same complex is also an active catalyst for the hydrosilylation of the CO and C≡N bonds of various ketones, aldehydes and α,β‐unsaturated nitriles. Hence, combination of these two properties permits development of a simple and proficient one‐flask, two‐step procedure for the deuterosilylation of these substrates.Ministerio de Ciencia y Tecnología CTQ2010‐17476, Consolider‐Ingenio 2010 CSD2007‐00006Junta de Andalucía FQM‐119, P09‐FQM‐4832Ministerio de Educación AP20080256CONACYT (Mexico) 2293

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

Electron-rich metal complexes for C02 and CS2 incorporation

The dihapto coordination of two molecules of carbon dioxide to a square-planar MoP2(P-P) fragment (P=monodentate-, P-P=bidentate phosphi- ne ligands) can occur in several ways giving rise to different conformers. Compounds of this type have been prepared and their spectroscopic proper- ties investigated by variable temperature 'H and 31P NMR studies. The for- mation of ethylene complexes related to Mo(C2H4)2(PMe3)4, 6, and the study of their reactivity towards carbon dioxide and carbon disulphide is also described. In particular, compound 6 induces a head-to-tail dimerization of carbon disulphide with formation of a Mo(II)-C$4 linkage, which, in the presence of carbon monoxide, undergoes a symmetric, oxidative rupture, which produces a Mo(0) complex and two molecules of carbon disulphide. The insertion reactions of carbon dioxide and other unsaturated molecules into the nickel-carbon bonds of the nickelacyclopentene complexes 9 have been investigated and different organic products isolated by means of simple or sequential insertion reactions.Ministerio de Educación y CienciaAgencia Nacional de Evaluación y Prospectiv

Synthesis and structural characterization of a binuclear iridium complex with bridging, bidentate N-heterocyclic carbene coordination of 2, 2 ':6 ', 2''-terpyridine

Thermal activation of terpyridine in the presence of an unsaturated Ir(III) fragment stabilized by a hydrotris(pyrazolyl) borate ligand gives rise to mononuclear complex 2 and binuclear 3, in which the polypyridine behaves, respectively, as a mono- or a bi-dentate N-heterocyclic carbene

An Unsaturated Four-Coordinate Dimethyl Dimolybdenum Complex with a Molybdenum–Molybdenum Quadruple Bond

We describe the synthesis and the molecular and electronic structures of the complex [Mo2Me2{μ‐HC(NDipp)2}2] (2; Dipp=2,6‐iPr2C6H3), which contains a dimetallic core with an Mo–Mo quadruple bond and features uncommon four‐coordinate geometry and has a fourteen‐electron count for each molybdenum atom. The coordination polyhedron approaches a square pyramid, with one of the molybdenum atoms nearly co‐planar with the basal square plane, in which the trans coordination position with respect to the Mo−Me bond is vacant. The other three sites are occupied by two trans nitrogen atoms of different amidinate ligands and the methyl group. The second Mo atom occupies the apex of the pyramid and forms an Mo–Mo bond of length 2.080(1) Å, consistent with a quadruple bond. Compound 2 reacts with tetrahydrofuran (THF) and trimethylphosphine to yield the mono‐adducts [Mo2Me(μ‐Me){μ‐HC(NDipp)2}2(L)] (3⋅THF and 3⋅PMe3, respectively) with one terminal and one bridging methyl group. In contrast, 4‐dimethylaminopyridine (dmap) forms the bis‐adduct [Mo2Me2{μ‐HC(NDipp)2}2(dmap)2] (4), with terminally coordinated methyl groups. Hydrogenolysis of complex 2 leads to the bis(hydride) [Mo2H2{μ‐HC(NDipp)2}2(thf)2] (5⋅THF) with elimination of CH4. Computational, kinetic, and mechanistic studies, which included the use of D2 and of complex 2 labelled with 13C (99 %) at the Mo–CH3 sites, supported the intermediacy of a methyl‐hydride reactive species. A computational DFT analysis of the terminal and bridging coordination of the methyl groups to the Mo≣Mo core is also reported.Ministerio de Ciencia e Innovación CTQ2010-15833, CTQ2013-42501-P, CTQ2014-52769-C3-3-R, CTQ2015-64579-C3-1-P, Consolider-Ingenio 2010 CSD2007-00006Junta de Andalucía FQM-119, P09-FQM-5117Ministerio de Educación AP-4193Ministerio de Ciencia e Innovación BES-2011-04764