Unmasking the constitution and bonding of the proposed lithium nickelate "LiNiPh(solv)": revealing the hidden CH ligand.

More than four decades ago, a complex identified as the planar homoleptic lithium nickelate "LiNiPh(solv)" was reported by Taube and co-workers. This and subsequent reports involving this complex have lain dormant since; however, the absence of an X-ray diffraction structure leaves questions as to the nature of the Ni-PhLi bonding and the coordination geometry at Ni. By systematically evaluating the reactivity of Ni(COD) with PhLi under different conditions, we have found that this classical molecule is instead a unique octanuclear complex, [{Li(solv)PhNi}(μ-η:η-CH)] (5).

Supported σ-Complexes of Li-C Bonds from Coordination of Monomeric Molecules of LiCH , LiCH CH and LiC H to Mo≣Mo Bonds.

LiCH and LiCH CH react with the complex [Mo (H) (μ-Ad ) (thf) ] (1⋅thf) with coordination of two molecules of LiCH R (R=H, CH ) and formation of complexes [Mo {μ-HLi(thf)CH R} (Ad ) ], 5⋅LiCH and 5⋅LiCH CH , respectively (Ad =HC(NDipp) ; Dipp=2,6- Pr C H ; thf=C H O). Due to steric hindrance, only one molecule of LiC H adds to 1⋅thf generating the complex [Mo (H){μ-HLi(thf)C H }(μ-Ad ) ], (4⋅LiC H ). Computational studies disclose the existence of five-center six-electron bonding within the H-Mo≣Mo-C-Li metallacycles, with a mostly covalent H-Mo≣Mo-C group and predominantly ionic Li-C and Li-H interactions.

Coordination of LiH Molecules to Mo≣Mo Bonds: Experimental and Computational Studies on MoLiH, MoLiH, and MoLiH Clusters.

The reactions of LiAlH as the source of LiH with complexes that contain (H)Mo≣Mo and (H)Mo≣Mo(H) cores stabilized by the coordination of bulky Ad ligands result in the respective coordination of one and two molecules of (thf)LiH, with the generation of complexes exhibiting one and two HLi(thf)H ligands extending across the Mo≣Mo bond (Ad = HC(NDipp); Dipp = 2,6-PrCH; thf = tetrahydrofuran, CHO). A theoretical study reveals the formation of Mo-H-Li three-center-two-electron bonds, supplemented by the coordination of the Mo≣Mo bond to the Li ion. Attempts to construct a [Mo{HLi(thf)H}(Ad)] molecular architecture led to spontaneous trimerization and the formation of a chiral, hydride-rich MoLiH supramolecular organization that is robust enough to withstand the substitution of lithium-solvating molecules of tetrahydrofuran by pyridine or 4-dimethylaminopyridine.

Experimental and Computational Studies on Quadruply Bonded Dimolybdenum Complexes with Terminal and Bridging Hydride Ligands.

This contribution focuses on complex [Mo (H) (μ-Ad ) ] (1) and tetrahydrofuran and pyridine adducts [Mo (H) (μ-Ad ) (L) ] (1⋅thf and 1⋅py), which contain a trans-(H)Mo≣Mo(H) core (Ad =HC(NDipp ) ; Dipp=2,6-iPr C H ). Computational studies provide insights into the coordination and electronic characteristics of the central trans-Mo H unit of 1, with four-coordinate, fourteen-electron Mo atoms and ϵ-agostic interactions with Dipp methyl groups. Small size C- and N-donors give rise to related complexes 1⋅L but only one molecule of P-donors, for example, PMe , can bind to 1, causing one of the hydrides to form a three-centered, two-electron (3c-2e) Mo-H→Mo bond (2⋅PMe ).

Molybdenum and tungsten complexes with carbon dioxide and ethylene ligands.

The first examples of stable metal complexes with coordinated ethylene and carbon dioxide ligands are reported. Reaction of tris(ethylene) complexes -M(CH)(PNP) (M = Mo and W; PNP = 2,6-bis(diphenylphosphinomethyl)pyridine) with CO yields the corresponding, mixed -M(CH)(CO)(PNP) derivatives. X-ray studies reveal six-coordinate structures exhibiting η-ethylene and κ-C,O carbon dioxide coordination.

Base-Promoted, Remote C-H Activation at a Cationic (η-CMe)Ir(III) Center Involving Reversible C-C Bond Formation of Bound CMe.

C-H bond activation at cationic [(η-CMe)Ir(PMeAr')] centers is described, where PMeAr' are the terphenyl phosphine ligands PMeAr and PMeAr. Different pathways are defined for the conversion of the five-coordinate complexes [(η-CMe)IrCl(PMeAr')], 2(Xyl) and 2(Dipp), into the corresponding pseudoallyls 3(Xyl) and 3(Dipp). In the absence of an external Brønsted base, electrophilic, remote ζ C-H activation takes place, for which the participation of dicationic species, [(η-CMe)Ir(PMeAr')], is proposed.

Synthesis, Structure and Nickel Carbonyl Complexes of Dialkylterphenyl Phosphines.

The experimental and computational characterization of a series of dialkylterphenyl phosphines, PR Ar' is described. The new P-donors comprise five compounds of general formula PR Ar (R=Me, Et, iPr, c-C H and c-C H ); Ar = 2,6-C H -(3,5-C H -(CMe ) ) ), and another five PR Ar' phosphines containing the bulky alkyl groups iPr, c-C H or c-C H , in combination with Ar'=Ar , Ar , or Ar (L1-L10). Steric and electronic parameters have been determined computationally and from IR and X-ray data obtained for the phosphines and for some derivatives, including tricarbonyl and dicarbonyl nickel complexes, Ni(CO) (PR Ar') and Ni(CO) (PR Ar').

Reactivity of a trans-[H-Mo[quadruple bond, length as m-dash]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.

Activation of Small Molecules by the Metal-Amido Bond of Rhodium(III) and Iridium(III) (η-CMe)M-Aminopyridinate Complexes.

We report the synthesis and structural characterization of five-coordinate complexes of rhodium and iridium of the type [(η-CMe)M(N^N)] (3-M), where N^N represents the aminopyridinate ligand derived from 2-NH(Ph)-6-(Xyl)CHN (Xyl = 2,6-MeCH). The two complexes were isolated as salts of the BAr anion (BAr = B[3,5-(CF)CH]). The M-N bond of complexes 3-M readily activated CO, CH, and H.

A Cationic Unsaturated Platinum(II) Complex that Promotes the Tautomerization of Acetylene to Vinylidene.

Complex [PtMe (PMe ArDipp2 )] (1), which contains a tethered terphenyl phosphine (ArDipp2 =2,6-(2,6- Pr C H ) C H ), reacts with [H(Et O) ]BAr (BAr =B[3,5-(CF ) C H ] ) to give the solvent (S) complex [PtMe(S)(PMe ArDipp2 )] (2⋅S). Although the solvent molecule is easily displaced by a Lewis base (e.g.

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 [Mo Me {μ-HC(NDipp) } ] (2; Dipp=2,6-iPr C H ), 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.

Methyl Complexes of the Transition Metals.

Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, that is, based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition-metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition-metal complexes containing M-CH3 fragments.

Methyl-, Ethenyl-, and Ethynyl-Bridged Cationic Digold Complexes Stabilized by Coordination to a Bulky Terphenylphosphine Ligand.

Reactions of the gold(I) triflimide complex [Au(NTf2 )(PMe2 Ar${{^{{\rm Dipp}{_{2}}}}}$)] (1) with the gold(I) hydrocarbyl species [AuR(PMe2 Ar${{^{{\rm Dipp}{_{2}}}}}$)] (2 a-2 c) enable the isolation of hydrocarbyl-bridged cationic digold complexes with the general composition [Au2 (μ-R)(PMe2 Ar${{^{{\rm Dipp}{_{2}}}}}$)2 ][NTf2 ], where Ar${{^{{\rm Dipp}{_{2}}}}}$=C6 H3 -2,6-(C6 H3 -2,6-iPr2 )2 and R=Me (3), CHCH2 (4), or CCH (5). Compound 3 is the first alkyl-bridged digold complex to be reported and features a symmetric [Au(μ-CH3 )Au](+) core. Complexes 4 and 5 are the first species of their kind that contain simple, unsubstituted vinyl and acetylide units, respectively.

Platinum(0) olefin complexes of a bulky terphenylphosphine ligand. Synthetic, structural and reactivity studies.

A novel terphenylphosphine PMe2Ar(Dipp2) () (Dipp = 2,6-(i)Pr2C6H3) forms stable Pt(0) complexes with ethene and 3,3-dimethylbut-1-ene that behave as sources of the reactive Pt(PMe2Ar(Dipp2)) fragment. The complexes are efficient catalysts for the selective hydrosilylation of terminal alkynes.

Lithium Di- and trimethyl dimolybdenum(II) complexes with Mo-Mo quadruple bonds and bridging methyl groups.

New dimolybdenum complexes of composition [Mo2{μ-Me}2Li(S)}(μ-X)(μ-N^N)2] (3a-3c), where S = THF or Et2O and N^N represents a bidentate aminopyridinate or amidinate ligand that bridges the quadruply bonded molybdenum atoms, were prepared from the reaction of the appropriate [Mo2{μ-O2CMe}2(μ-N^N)2] precursors and LiMe. For complex 3a, X = MeCO2, while in 3b and 3c, X = Me. Solution NMR studies in C6D6 solvent support formulation of the complexes as contact ion pairs with weak agostic Mo-CH3···Li interactions, which were also evidenced by X-ray crystallography in the solid-state structures of the molecules of 3a and 3b.

Water-Promoted Generation of a Diazairida Homobarrelene by C-C Coupling Between an Iridacyclic Alkylidene and Acetonitrile.

The stable cationic iridacyclopentenylidene [Tp(Me2)Ir(=CHC(Me)=C(Me)CH2(NCMe)]PF6 (A; Tp(Me2)=hydrotris(3,5-dimethylpyrazolyl)borate) has been obtained by α-hydride abstraction from the iridacyclopent-2-ene [Tp(Me2)Ir(CH2C(Me)=C(Me)CH2)(NCMe)]. Complex A exhibits Brønsted-Lowry acidity at the Ir-CH2 and proximal (relative to Ir-CH2 ) methyl sites. The coordination of an extra molecule of acetonitrile to the iridium center initiates the reversible isomerization of the chelating carbon chain of A to the monodentate butadienyl ligand of complex [Tp(Me2)Ir(CH=C(Me)C(Me)=CH2)(NCMe)2]PF6, which is capable to engage in a water-promoted C-C coupling with the MeCN co-ligands.

Synthesis and Reactivity toward H2 of (η(5)-C5Me5)Rh(III) Complexes with Bulky Aminopyridinate Ligands.

Electrophilic, cationic Rh(III) complexes of composition [(η(5)-C5Me5)Rh(Ap)](+), (1(+)), were prepared by reaction of [(η(5)-C5Me5)RhCl2]2 and LiAp (Ap = aminopyridinate ligand) followed by chloride abstraction with NaBArF (BArF = B[3,5-(CF3)2C6H3]4). Reactions of cations 1(+) with different Lewis bases (e.g.

Reactivity of cationic agostic and carbene structures derived from platinum(II) metallacycles.

This paper describes the formation of new platinacyclic complexes derived from the phosphine ligands PiPr2 Xyl, PMeXyl2 , and PMe2 Ar Xyl 2 (Xyl=2,6-Me2 C6 H3 and Ar Xyl 2=2,6-(2,6-Me2 C6 H3 )2 -C6 H3 ) as well as reactivity studies of the trans-[Pt(C^P)2 ] bis-metallacyclic complex 1 a derived from PiPr2 Xyl. Protonation of compound 1 a with [H(OEt2 )2 ][BArF ] (BArF =B[3,5-(CF3 )2 C6 H3 ]4 ) forms a cationic δ-agostic structure 4 a, whereas α-hydride abstraction employing [Ph3 C][PF6 ] produces a cationic platinum carbene trans-[Pt{PiPr2 (2,6-CH(Me)C6 H3 }{PiPr2 (2,6-CH2 (Me)C6 H3 }][PF6 ] (8). Compounds 4 a and 8 react with H2 to yield the same 1:3 equilibrium mixture of 4 a and trans-[PtH(PiPr2 Xyl)2 ][BArF ] (6), in which one of the phosphine ligands participates in a δ-agostic interaction.

Dihydrogen catalysis of the reversible formation and cleavage of C-H and N-H bonds of aminopyridinate ligands bound to (η(5) -C5 Me5 )Ir(III.).

This study focuses on a series of cationic complexes of iridium that contain aminopyridinate (Ap) ligands bound to an (η(5) -C5 Me5 )Ir(III) fragment. The new complexes have the chemical composition [Ir(Ap)(η(5) -C5 Me5 )](+) , exist in the form of two isomers (1(+) and 2(+) ) and were isolated as salts of the BArF (-) anion (BArF =B[3,5-(CF3 )2 C6 H3 ]4 ). Four Ap ligands that differ in the nature of their bulky aryl substituents at the amido nitrogen atom and pyridinic ring were employed.

Experimental and computational studies of the molybdenum-flanking arene interaction in quadruply bonded dimolybdenum complexes with terphenyl ligands.

To clarify the nature of the Mo-Carene interaction in terphenyl complexes with quadruple Mo-Mo bonds, ether adducts of composition [Mo2 (Ar')(I)(O2 CR)2 (OEt2)] have been prepared and characterized (Ar'=Ar(Xyl) 2 , R=Me; Ar'=ArMes2, R=Me; Ar'=Ar(Xyl2), R=CF3) (Mes=mesityl; Xyl=2,6-Me2 C6 H3, from now on xylyl) and their reactivity toward different neutral Lewis bases investigated. PMe3 , P(OMe)3 and PiPr3 were chosen as P-donors and the reactivity studies complemented with the use of the C-donors CNXyl and CN2 C2 Me4 (1,3,4,5-tetramethylimidazol-2-ylidene). New compounds of general formula [Mo2 (Ar')(I)(O2 CR)2 (L)] were obtained, except for the imidazol-2-ylidene ligand that yielded a salt-like compound of composition [Mo2 (Ar(Xyl2))(O2 CMe)2 (CN2 C2 Me4)2]I.

Terphenyl complexes of molybdenum and tungsten with quadruple metal-metal bonds and bridging carboxylate ligands.

Mono- and bis-terphenyl complexes of molybdenum and tungsten with general composition M2(Ar')(O2CR)3 and M2(Ar')2(O2CR)2, respectively (Ar' = terphenyl ligand), that contain carboxylate groups bridging the quadruply bonded metal atoms, have been prepared and structurally characterized. The new compounds stem from the reactions of the dimetal tetracarboxylates, M2(O2CR)4 (M = Mo, R = H, Me, CF3; M = W, R = CF3) with the lithium salts of the appropriate terphenyl groups (Ar' = Ar(Xyl2), Ar(Mes2), Ar(Dipp2), and Ar(Trip2)). Substitution of one bidentate carboxylate by a monodentate terphenyl forms a M-C σ bond and creates a coordination unsaturation at the other metal atom.

Experimental and theoretical studies on arene-bridged metal-metal-bonded dimolybdenum complexes.

The bis(hydride) dimolybdenum complex, [Mo2(H)2{HC(N-2,6-iPr2C6H3)2}2(thf)2], 2, which possesses a quadruply bonded Mo2(II) core, undergoes light-induced (365 nm) reductive elimination of H2 and arene coordination in benzene and toluene solutions, with formation of the Mo(I)2 complexes [Mo2{HC(N-2,6-iPr2C6H3)2}2(arene)], 3⋅C6H6 and 3⋅C6H5Me, respectively. The analogous C6H5OMe, p-C6H4Me2, C6H5F, and p-C6H4F2 derivatives have also been prepared by thermal or photochemical methods, which nevertheless employ different Mo2 complex precursors. X-ray crystallography and solution NMR studies demonstrate that the molecule of the arene bridges the molybdenum atoms of the Mo(I)2 core, coordinating to each in an η(2) fashion.

Cyclometalated iridium complexes of bis(aryl) phosphine ligands: catalytic C-H/C-D exchanges and C-C coupling reactions.

This work details the synthesis and structural identification of a series of complexes of the (η(5)-C5Me5)Ir(III) unit coordinated to cyclometalated bis(aryl)phosphine ligands, PR'(Ar)2, for R' = Me and Ar = 2,4,6-Me3C6H2, 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-C6H3(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.

Reactivity studies of iridium pyridylidenes [Tp(Me2)Ir(C(6)H(5))(2)(C(CH)(3)C(R)NH] (R=H, Me, Ph).

The reactivity of a series of iridiumpyridylidene complexes with the formula [Tp(Me2) Ir(C6 H5 )2 (C(CH)3 C(R)NH] (1 a-1 c) towards a variety of substrates, from small molecules, such as H2 , O2 , carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e(-) unsaturated [Tp(Me2) Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H2 is heterolytically split to give hydridepyridylidene complexes, whilst CO, CO2 , and H2 CO provide carbonyl, carbonate, and alkoxide species, respectively.