Bridging Carbene Research Articles

Four-Membered Bimetallic Carbon Complex [(MCp*)2(μ-NPh)(μ-C)] (M = Fe, Ru, Os) - An Ambiphilic Carbene with Lone Pair and σ-Hole Reactivity.

Singlet carbenes are extensively studied compounds capable of electrophilic, nucleophilic or ambiphillic behaviour. The ambiphilic reactivity of singlet carbenes have been conventionally observed in orthogonal planes. Here, we report a detailed bonding and reactivity study of a homobimetallic carbon complex [(MCp*)2(μ-NPh)(μ-C)] (1M, M = Fe, Ru, Os) that shows ambiphilicity in the same direction. The structure of this complex can be considered as two fused three-membered M-C-M and M-N-M rings. The bonding analysis suggests that these 17VE homobimetallic complexes have one formal M-M bond with a bridging carbene centre featuring a high lying spn-hybridised lone pair. Accordingly, the carbene centre shows high proton affinity and act as a good 2e- donor to Lewis acids and transition metal fragment. Apart from the transition metal non-bonding electrons, the π-framework of M-C-M and M-N-M arms can be best described as 3c-2e- bonds. The two transition metals in the four-membered skeleton generate many low-lying, virtual orbitals. These low-lying virtual orbitals induces electron excitation from the spn-hybrid orbital in presence of H- and other 2e- donor ligands such as PMe3, NHC and CO. Hence, the spn-hybrid lone pair orbital shows σ-hole reactivity in presence of Lewis bases.

Deoxygenation of nitrosoarene by N-heterocyclic carbene (NHC): an elusive Breslow-type intermediate bridging carbene and nitrene.

N-Heterocyclic carbene (NHC) activates and deoxygenates nitrosoarene (ArNO) to afford arylnitrene (ArN), thereby portraying a fundamental route connecting two 6e- species. A combination of spectroscopic and computational studies suggests that the interaction of ArNO with NHC affords a transient 2,2'-diamino imine-N-oxide as a key intermediate in ArNO deoxygenation.

Oxidative addition of methylene chloride to Me-DuPhos complexes of palladium and rhodium

Oxidative addition of methylene chloride to Pd((R,R)-Me-DuPhos)(L) (1–3; L = P(t-Bu)3, PCy3, or trans-stilbene) gave Pd((R,R)-Me-DuPhos)(CH2Cl)(Cl) (4). Treatment of [Rh(COD)(Cl)]2 with (R,R)-Me-DuPhos at low temperature in THF or CH2Cl2 afforded [Rh((R,R)-Me-DuPhos)(Cl)]2 (5). At room temperature, these reactions also gave the byproduct [Rh((R,R)-Me-DuPhos)2][Cl], which was prepared independently as the BF4 salt 6. When 5 was generated in CH2Cl2, oxidative addition of both CCl bonds yielded the bridging carbene complex (Rh((R,R)-Me-DuPhos)(Cl))2(µ-Cl)2(µ-CH2) (8). Both 6 and 8 were crystallographically characterized.

Carbene Formation and Transfer at a Dinickel Active Site.

The synthesis and reactivity of a dinickel bridging carbene is described. The previously reported [ i-PrNDI]Ni2(C6H6) complex (NDI = naphthyridine-diimine) reacts with Ph2CN2 to generate a metastable diazoalkane adduct, which eliminates N2 at 60 °C to yield a paramagnetic Ni2(μ-CPh2) complex. The Ni2(μ-CPh2) complex undergoes carbene transfer to t-BuNC via an initial isonitrile adduct, which, upon heating, releases free t-BuNCCPh2. Based on this sequence of stoichiometric reactions, a catalytic carbene transfer reaction is demonstrated.

Photoinduced Reactions of Diruthenium Tetrahydride Complexes: Carbon–Hydrogen Bond Cleavage of Tetrahydrofuran Leading to Bridging Cyclic Fischer-Type Carbene Complexes

Photochemical reactions of diruthenium tetrahydride complexes containing cyclopentadienyls as auxiliary ligands, CpsRu(μ-H)4RuCps (1) (a: Cps = C5Me5 (Cp*), b: C5EtMe4 (CpEt), and c: 1,2,4-C5(t-Bu)3H2 (Cp‡)), with tetrahydrofuran were studied for elucidation of the reaction mode of dinuclear complexes containing multiple bridging hydrides. Complexes 1a–c reacted with tetrahydrofuran under UV irradiation (365 nm) to produce bridging cyclic Fischer-type carbene complexes, {CpsRu(μ-H)}2(μ-cyclo-CCH2CH2CH2O−)(μ-H)2 (5), via consecutive C–H bond cleavage at the α-position of the oxygen atom. The characteristic cyclic structures of the bridging carbene ligands were unambiguously confirmed by X-ray diffraction studies. Line-shape analysis of the variable-temperature 1H NMR spectra of 5c demonstrated the rotation of the bridging carbene ligand.

Contributions to the Chemistry of the Cyclopentadienyl Complex [Cp∧RuCl2]2 (“Cp‐roof” = η5‐1‐Methoxy‐2,4‐tert‐butyl‐3‐neopentylcyclopentadienyl)

Abstract The dimeric ruthenium complex [Cp∧RuCl2]2 is easily accessible in a one‐pot reaction from RuCl3(solv)n and tert‐butylacetylene. It features sterically very demanding “Cp‐roof” ligands (Cp∧ = η5‐1‐methoxy‐2,4‐tert‐butyl‐3‐neopentylcyclopentadienyl), which impart a unique reactivity. Herein we describe the synthesis and the characterization of novel Cp∧Ru complexes bearing a bridging carbene ligand, a linear imido ligand, or an orthometalated phosphine ligand. Furthermore, the microwave‐assisted syntheses of the bimetallic complexes [Cp∧Ru(μ‐Cl)3Ru(p‐cymene)] and [Cp∧Ru(μ‐Cl)3RhCp*] are described.

‘Carbene Radicals’ in CoII(por)-Catalyzed Olefin Cyclopropanation

The mechanism of cobalt(II)-porphyrin-mediated cyclopropanation of olefins with diazoesters was studied. The first step--reaction of cobalt(II)-porphyrin with ethyl diazoacetate (EDA)--was examined using EPR and ESI-MS techniques. EDA reacts with cobalt(II)-porphyrin to form a 1:1 Co(por)(CHCOOEt) adduct that exists as two isomers: the 'bridging carbene' C' in which the 'carbene' is bound to the metal and the pyrrolic nitrogen of the porphyrin that has a d(7) configuration on the metal, and the 'terminal carbene' C in which the 'carbene' behaves as a redox noninnocent ligand having a d(6) cobalt center and the unpaired electron residing on the 'carbene' carbon atom. The subsequent reactivities of the thus formed 'cobalt carbene radical' with propene, styrene, and methyl acrylate were studied using DFT calculations. The calculations suggest that the formation of the carbene is the rate-limiting step for the unfunctionalized Co(II)(por) and that the cyclopropane ring formation proceeds via a stepwise radical process: Radical addition of the 'carbene radical' C to the C=C double bonds of the olefins results in formation of the gamma-alkyl radical intermediates D. Species D then easily collapse in almost barrierless ring-closure reactions (TS3) to form the cyclopropanes. This radical mechanism readily explains the high activity of Co(II)(por) species in the cyclopropanation of electron-deficient olefins such as methyl acrylate.

Thermolytic Products Derived from Thermolysis of Cycloolefin-Coordinated Diiron Bridging Carbene Complexes

Heating a benzene solution of the COT-coordinated diiron bridging alkoxycarbene complexes [Fe2{μ-C(OC2H5)Ar}(CO)4(η8-C8H8)] (1, Ar = C6H5; 2, Ar = p-CH3C6H4; 3, Ar = p-CF3C6H4) in a sealed tube at 85−90 °C for 72 h gave the bicycloolefin-coordinated tricarbonyliron dimers [Fe{η4-C9H8(Ar}(CO)3]2 (10, Ar = C6H5; 12, Ar = p-CH3C6H4; 14, Ar = p-CF3C6H4) and bridging arylcarbene complexes [Fe2{μ-C(H)Ar}(CO)4(η8-C8H8)] (11, Ar = C6H5; 13, Ar = p-CH3C6H4; 15, Ar = p-CF3C6H4). A similar thermolysis of 7H-indene-coordinated diiron bridging alkoxycarbene complex [Fe2{μ-C(OC2H5)C6H5}(CO)4(η4,η4-C9H8)] (4) yielded the ring addition product [Fe2{C(OC2H5)C6H5(η2,η5-C9H8)}(CO)5] (16). The 7H-indene-coordinated diiron bridging arylthiocarbene complexes [Fe2{μ-C(Ar)SC6H4CH3-p}(CO)4(η4,η4-C9H8)] (8, Ar = C6H5; 9, Ar = p-C6H5C6H4) were heated similarly to afford the isomerized 7H-indene-coordinated diiron bridging carbene complexes with a μ-SC6H4CH3-p ligand, [Fe2{μ-C(Ar)(η2,η5-C9H8)}(μ-SC6H4CH3-p)(CO)3] (17, Ar = C6H5; 19, Ar = p-C6H5C6H4), and the acyliron compounds [Fe(CO)2(CO){C(H)Ar(η5-C9H8)}] (18, Ar = C6H5; 20, Ar = p-C6H5C6H4). The structures of complexes 14, 16, 17, and 18 have been established by X-ray diffraction studies.

Gold(i)–carbenes derived from 4-pyridylisocyanide complexes: supramolecular macrocycles supported by hydrogen bonds, and luminescent behavior

Monomeric gold(I) carbenes of the type [AuR[C(NR1R2)(NHPy-4)]] (Py-4 = 4-pyridyl) have been prepared with R = C6F5, Fmes (2,4,6-tris(trifluoromethyl)phenyl) by reaction of the corresponding isocyanide compounds [AuR(CNPy-4)] with primary or secondary amines. The single crystal X-ray diffraction structures of [Au(C6F5)[C(NEt2)(NHPy-4)]].OH2, [Au(Fmes)[C(NEt2)(NHPy-4)]], and [Au(Fmes)[C(NHMe)(NHPy-4)]] show that the presence of the NHPy-4 moiety formed induces the formation of supramolecular macrocycles only supported by hydrogen bond interactions, either with N-H groups of other molecules (tetrameric macrocycles), or with water molecules (dimeric macrocycles). Dimeric gold(I) carbenes were also produced using a diamine to form a bridging carbene, or using octafluorobiphenyl to form a Au-C6F4-C6F4-Au bridge, but the solid state structures of these dimers could not be solved. Most of the complexes herein described display luminescent properties.

Syntheses, structures and reactivities of diindenyl-coordinated diiron bridging carbene complexes

Compound [Fe 2(μ-CO) 2(CO) 2(η 5-C 9H 7) 2] ( 1) reacts with aryllithium reagents, ArLi (Ar = C 6H 5, p-CH 3C 6H 4, p-CF 3C 6H 4) followed by alkylation with Et 3OBF 4 to give the diindenyl-coordinated diiron bridging alkoxycarbene complexes [Fe 2{μ-C(OC 2H 5)Ar}(μ-CO)(CO) 2(η 5-C 9H 7) 2] ( 2, Ar = C 6H 5; 3, Ar = p-CH 3C 6H 4, 4, Ar = p-CF 3C 6H 4). Complex 4 reacts with HBF 4 · Et 2O at low temperature to yield cationic bridging carbyne complex [Fe 2(μ-CC 6H 4CF 3- p)(μ-CO)(CO) 2(η 5-C 9H 7) 2]BF 4 ( 5). Cationic 5 reacts with NaBH 4 in THF at low temperature to afford diiron bridging arylcarbene complex [Fe 2{μ-C(H)C 6H 4CF 3- p}(μ-CO)(CO) 2(η 5-C 9H 7) 2] ( 6). The reaction of 5 with NaSC 6H 4CH 3- p under the similar conditions gave the bridging arylthiocarbene complex [Fe 2{μ-C(C 6H 4CF 3- p)SC 6H 4CH 3- p}(μ-CO)(CO) 2(η 5-C 9H 7) 2] ( 7). Complex 5 can also react with carbonylmetal anionic compounds Na[M(CO) 5(CN)] (M = Cr, Mo, W) to produce the diiron bridging aryl(penta-carbonylcyanometal)carbene complexes [Fe 2{μ-C(C 6H 4CF 3- p)NCM(CO) 5}(μ-CO)(CO) 2(η 5-C 9H 7) 2] ( 8, M = Cr; 9, M = Mo; 10, M = W). The structures of complexes 4, 6, 7, and 10 have been established by X-ray diffraction studies.

Novel dimetal bridging carbene complexes derived from a terminal carbonyl dimetal compound. Syntheses, structures and reactivities of 7H-indene-coordinated diiron bridging carbene complexes

Pentacarbonyl-7H-indenediiron, [Fe2(CO)5(eta3,eta5-C9H8)] (1), reacts with aryllithium, ArLi (Ar = C6H5, p-C6H5C6H4), followed by alkylation with Et3OBF4 to give novel 7H-indene-coordinated diiron bridging alkoxycarbene complexes [Fe2{mu-C(OC2H5)Ar}(CO)4(eta4,eta4-C9H8)] (2, Ar = C6H5; 3, Ar = p-C6H5C6H4). Complexes 2 and 3 react with HBF4.Et2O at low temperature to yield cationic bridging carbyne complexes [Fe2(mu-CAr)(CO)4(eta4,eta4-C9H8)]BF4 (4, Ar = C6H5; 5, Ar = p-C6H5C6H4). Cationic 4 and 5 react with NaBH4 in THF at low temperature to afford diiron bridging arylcarbene complexes [Fe2{mu-C(H)Ar}(CO)4(eta4,eta4-C9H8)] (6, Ar = C6H5; 7, Ar = p-C6H5C6H4). The similar reactions of 4 and 5 with NaSC6H4CH3-p produce the bridging arylthiocarbene complexes [Fe2{mu-C(Ar)SC6H4CH3-p}(CO)4(eta4,eta4-C9H8)] (8, Ar = C6H5; 9, Ar = p-C6H5C6H4). Cationic 4 and 5 can also react with anionic carbonylmetal compounds Na[M(CO)5(CN)] (M = Cr, Mo, W) to give the diiron bridging aryl(pentacarbonylcyanometal)carbene complexes [Fe2{mu-C(Ar)NCM(CO)5}(CO)4(eta4,eta4-C9H8)] (10, Ar = C6H5, M = Cr; 11, Ar = p-C6H5C6H4, M = Cr; 12, Ar = C6H5, M = Mo; 13, Ar = p-C6H5C6H4, M = Mo; 14, Ar = C6H5, M = W; 15, Ar = p-C6H5C6H4, M = W). Interestingly, in CH2Cl2 solution at room temperature complexes 10-15 were transformed into the isomerized 7H-indene-coordinated monoiron complexes [Fe(CO)2(eta5-C9H8)C(Ar)NCM(CO)5] (16, Ar = C6H5, M = Cr; 17, Ar = p-C6H5C6H4, M = Cr; 18, Ar = C6H5, M = Mo; 19, Ar = p-C6H5C6H4, M = Mo; 20, Ar = C6H5, M = W; 21, Ar = p-C6H5C6H4, M = W), while complex 3 was converted into a novel ring addition product [Fe2{C(OC2H5)C6H4C6H5-p-(eta2,eta5-C9H8)}(CO)5] (22) under the same conditions. The structures of complexes 2, 6, 8, 14, 18 and 22 have been established by X-ray diffraction studies.

Synthesis, structure and reactivity of novel pyridazine-coordinated diiron bridging carbene complexes

[{mu-(Pyridazine-N(1):N(2))}Fe(2)(mu-CO)(CO)(6)](1) reacts with aryllithium reagents, ArLi (Ar = C(6)H(5), m-CH(3)C(6)H(4)) followed by treatment with Me(3)SiCl to give the novel pyridazine-coordinated diiron bridging siloxycarbene complexes [(C(4)H(4)N(2))Fe(2){mu-C(OSiMe(3))Ar}(CO)(6)](2, Ar = C(6)H(5); 3, Ar =m-CH(3)C(6)H(4)). Complex 2 reacts with HBF(4).Et(2)O at low temperature to yield a cationic bridging carbyne complex [(C(4)H(4)N(2))Fe(2)(mu-CC(6)H(5))(CO)(6)]BF(4)(4). Cationic 4 reacts with NaBH(4) in THF at low temperature to afford the diiron bridging arylcarbene complex [(C(4)H(4)N(2))Fe(2){mu-C(H)C(6)H(5)}(CO)(6)](5). Unexpectedly, the reaction of 4 with NaSCH(3) under similar conditions gave the bridging arylcarbene complex 5 and a carbonyl-coordinated diiron bridging carbene complex [Fe(2){mu-C(SCH(3))C(6)H(5)}(CO)(7)](6), while the reaction of NaSC(6)H(4)CH(3)-p with 4 affords the expected bridging arylthiocarbene complex [(C(4)H(4)N(2))Fe(2){mu-C(SC(6)H(4)CH(3)-p)C(6)H(5)}(CO)(6)](7), which can be converted into a novel diiron bridging carbyne complex with a thiolato-bridged ligand, [Fe(2)(mu-CC(6)H(5))(mu-SC(6)H(4)CH(3)-p)(CO)(6)](8). Cationic can also react with the carbonylmetal anionic compound Na(2)[Fe(CO)(4)] to yield complex 5, while the reactions of 4 with carbonylmetal anionic compounds Na[M(CO)(5)(CN)](M = Cr, Mo, W) produce the diiron bridging aryl(pentacarbonylcyanometal)carbene complexes [(C(4)H(4)N(2))Fe(2)-{mu-C(C(6)H(5))NCM(CO)(5)}(CO)(6)](9, M = Cr; 10, M = Mo; 11, M = W). The structures of complexes 2, 5, 6, 8, and 9 have been established by X-ray diffraction studies.

Remarkable reactions of cyclooctatetraene diiron-bridging carbyne complexes with amino and amido compounds: nucleophilic addition to and breaking of the cyclooctatetraene ring.

The reactions of the cationic, diiron-bridging carbyne complexes [Fe(2)(mu-CAr)(CO)(4)(eta(8)-C(8)H(8))]BF(4) (1, Ar=C(6)H(5); 2, Ar=p-CH(3)C(6)H(4); 3, Ar=p-CF(3)C(6)H(4)) with LiN(C(6)H(5))(2) in THF at low temperature gave novel N-nucleophilic-addition products, namely, the neutral, diiron-bridging carbyne complexes [Fe(2)(mu-CAr)(CO)(4)(eta(7)-C(8)H(8)N(C(6)H(5))(2))] (4, Ar=C(6)H(5); 5, Ar=p-CH(3)C(6)H(4); 6, Ar=p-CF(3)C(6)H(4))). Cationic bridging carbyne complexes 1-3 react with (C(2)H(5))(2)NH, (iC(3)H(7))(2)NH, and (C(6)H(11))(2)NH under the same conditions with ring cleavage of the COT ligand to produce the novel diiron-bridging carbene inner salts [Fe(2)[mu-C(Ar)C(8)H(8)NR(2)](CO)(4)] (7, Ar=C(6)H(5), R=C(2)H(5); 8, Ar=p-CH(3)C(6)H(4), R=C(2)H(5); 9, Ar=p-CF(3)C(6)H(4), R=C(2)H(5); 10, Ar=C(6)H(5), R=iC(3)H(7); 11, Ar=p-CH(3)C(6)H(4), R=iC(3)H(7); 12, Ar=p-CF(3)C(6)H(4), R=iC(3)H(7); 13, Ar=C(6)H(5), R=C(6)H(11); 14, Ar=p-CH(3)C(6)H(4), R=C(6)H(11), 15, Ar=p-CF(3)C(6)H(4), R=C(6)H(11)). Piperidine reacts similarly with cationic carbyne complex 3 to afford the corresponding bridging carbene inner salt [Fe(2)[mu-C(Ar)C(8)H(8)N(CH(2))(5)](CO)(4)] (16). Compound 9 was transformed into a new diiron-bridging carbene inner salt 17, the trans isomer of 9, by heating in benzene. Unexpectedly, the reaction of C(6)H(5)NH(2) with 2 gave a novel COT iron-carbene complex [Fe(2)[=C(C(6)H(4)CH(3)-p)NHC(6)H(5)](mu-CO)(CO)(3)(eta(8)-C(8)H(8))] (18). However, the analogous reactions of 2-naphthylamine with 2 and of p-CF(3)C(6)H(4)NH(2) with 3 produce novel chelated iron-carbene complexes [Fe(2)[=C(C(6)H(4)CH(3)-p)NC(10)H(7)](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (19) and [Fe(2)[=C(C(6)H(4)CF(3)-p)NC(6)H(4)CF(3)-p](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (20), respectively. Compound 18 can also be transformed into the analogous chelated iron-carbene complex [Fe(2)[=C(C(6)H(4)CH(3)-p)NC(6)H(5)](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (21). The structures of complexes 6, 9, 15, 17, 18, and 21 have been established by X-ray diffraction studies.

Novel N-Nucleophilic Addition to and Ring-Breaking of Coordinated Cyclooctatetraene in Diiron Bridging Carbyne Complexes

The reactions of the diiron cationic carbyne complexes 1−3 with NaN(SiMe3)2 or LiN(SiMe3)2 in THF at low temperature give novel N-nucleophilic addition products, the neutral diiron bridging carbyne complexes 4−6, while the reactions of 1−3 with LiNEt2 lead to breaking of the COT ring to produce the diiron bridging carbene inner salts 7−9, among which the structures of 4 and 7 have been established by X-ray diffraction studies.

Unusual Reactions of Cationic Bridging Carbyne Complexes of Dimethylsilane-Bridged Bis(η5-cyclopentadienyl)diiron Tricarbonyl with Nucleophiles. A Route to Iron−Sulfur Cluster Bridging Carbene Complexes

The reactions of diiron cationic carbyne complexes [Fe2(μ-CO)(μ-CAr)(CO)2{(η5-C5H4)2Si(CH3)2}]BBr4 (4, Ar = C6H5; 5, Ar = p-CH3C6H4; 6, Ar = p-CF3C6H4) with NaSR (R = CH3, C6H5, p-CH3C6H4) in THF at low temperature afford diiron bridging mercaptocarbene complexes [Fe2(μ-CO){μ-C(SR)Ar}(CO)2{(η5-C5H4)2Si(CH3)2}] (9, Ar = C6H5, R = CH3; 10, Ar = C6H5, R = C6H5; 11, Ar = C6H5, R = p-CH3C6H4; 12, Ar = p-CH3C6H4, R = CH3; 13, Ar = p-CH3C6H4, R = C6H5;14, Ar = p-CH3C6H4, R = p-CH3C6H4; 15, Ar = p-CF3C6H4, R = CH3; 16, Ar= p-CF3C6H4, R = C6H5; 17, Ar = p-CF3C6H4, R = p-CH3C6H4). Compound 6 reacts with [(μ-SLi)(μ-SC6H5)Fe2(CO)6] to give the novel iron−sulfur cluster bridging carbene complex [Fe2(μ-CO)(μ-CC6H4CF3-p)(CO)2{(η5-C5H4)2Si(CH3)2}(μ-S)(μ-SC6H5)Fe2(CO)6] (18). Analogous iron−sulfur cluster bridging carbene complexes [Fe2(μ-CO)(μ-CAr)(CO)2(η5-C5H5)2(μ-S)(μ-SC6H5)Fe2(CO)6] (19, Ar = C6H5; 20, Ar = p-CH3C6H4) can also be obtained by the reactions of diiron cationic carbyne complexes [Fe2(μ-CO)(μ-CAr)(CO)2(η5-C5H5)2]BBr4 (7, Ar = C6H5; 8, Ar = p-CH3C6H4) with [(μ-SLi)(μ-SC6H5)Fe2(CO)6]. The structures of complexes 9, 13, 16, and 18 have been established by X-ray crystallography.

Formation of Cyclopentadienyl and Ruthenacyclopentadienyl Derivatives through Ynenyl-Diyne and Ynenyl-Alkyne Couplings onto a Triruthenium Cluster Core

The compound [Ru3(mu-H)(mu3-eta2-ampy)(CO)9] (1; Hampy =2-amino-6-methylpyridine) reacts with diynes RC4R in THF at reflux temperature to give the ynenyl derivatives [Ru3(mu3-eta2-ampy)(mu-eta3-RC...CC-CHR)(mu-CO)2-(CO)6] (2: R=CH2OPh; 3: R=Ph). These products contain a 1,4-disubstituted butynen-3-yl ligand attached to two ruthenium atoms. The compound [Ru3(mu-eta2-ampy)[mu3-eta6-PhCC5(C...CPh)-HPh2](CO)7] (4), which contains an eta5-cyclopentadienyl ring and a bridging carbene fragment, has also been obtained from the reaction of 1 with diphenylbutadiyne. This compound arises from a remarkable [3+2] cycloaddition reaction of a preformed 1,4-diphenylbutynen-4-yl ligand with a triple bond of a second diphenylbutadiyne molecule. The reactivity of the ynenyl derivatives 2 and 3 with diynes and alkynes has been studied. In all cases, compounds of the general formula [Ru3(mu-eta2-ampy)[mu3-eta5-C(=CHR)C=CRCR1=CR2](CO)7] (5-17) have been obtained. They all contain a ruthenacyclopentadienyl fragment formed by coupling of the coordinated ynenyl ligand of 2 (R = CH2OPh) or 3 (R = Ph) with a triple bond of the new reagent (the CR1=CR2 fragment results from the incoming diyne or alkyne reagent). While most of the products derived from 2 have the alkenyl C=CHR fragment with a Z configuration (R cis to Ru), all the compounds obtained from 3 have this fragment with an E configuration. Except 2 and 3, all the cluster complexes described in this article have a five-electron donor ampy ligand attached to only two metal atoms, a coordination mode unprecedented in cluster chemistry.

Remarkable Reactions of Cationic Carbyne Complexes of Manganese and Rhenium with Diiron Anions [Fe2(μ-CO)(μ-SeR)(CO)6]-. A Route to RSe-Bridged Dimetal Bridging Carbene Complexes

The reactions of cationic carbyne complexes of manganese and rhenium, [η-C5H5(CO)2M⋮CC6H5]BBr4 (1, M = Mn; 2, M = Re), with diiron anionic compounds [Et3NH][Fe2(μ-CO)(μ-SeR)(CO)6] (3, R = C6H5; 4, R = p-CH3C6H4) in THF at low temperature gave the dimetal bridging carbene complexes [MFe{μ-C(SeR)C6H5}(CO)5(η-C5H5)] (10, M = Mn, R = C6H5; 11, M = Mn, R = p-CH3C6H4; 13, M = Re, R = C6H5; 14, M = Re, R = p-CH3C6H4), [η-C5H5M(CO)3] (7, M = Mn; 12, M = Re), and [Fe2(μ-SeR)2(CO)6] (8, R = C6H5; 9, R = p-CH3C6H4). Complexes 1 and 2 also react with [MgBr][Fe2(μ-CO)(μ-SeC2H5)(CO)6] (5) to produce [Fe2(μ-SeC2H5)2(CO)6] (15) and dimetal bridging carbene complexes [MnFe{μ-C(SeC2H5)C6H5}(CO)5(η-C5H5)] (17) and [ReFe{μ-C(SeC2H5)C6H5}(CO)5(η-C5H5)] (18), respectively. 2 reacts similarly with [MgBr][Fe2(μ-CO)(μ-SeC4H9-n)(CO)6] (6) to give [Fe2(μ-SeC4H9-n)2(CO)6] (16) and a Re−Fe bridging carbene complex [ReFe{μ-C(SeC4H9-n)C6H5}(CO)5(η-C5H5)] (19), while the analogous reaction of 1 with 6 produced an unexpected trimetal bridging carbyne complex [MnFe2(μ-H)(μ-CO)2(μ3-CC6H5)CO)6(η-C5H5)] (20). The structures of complexes 9, 10, 13, 18, and 20 have been established by X-ray diffraction studies.

Early transition metal and lanthanide bis(iminophosphorano)methandiide complexes; ‘pincer’ and bridging bis(phosphorus) metal carbenes

The spontaneous double deprotonation of bis(iminophosphorano)methane ligands with alkyl or bis(trimethylsilyl)amido metal precursors yields ‘pincer’ carbenes of Group 4 and lanthanide metals. The generality of the system is extended with the dilithiumbis(iminophosphorano)methandiide salt which is obtained by lithiating bis(trimethylsilylimino(diphenylphosphorano))methane with two moles of lithium alkyl. This dilithium salt reacts with metal halides with metathetical elimination of LiCl to access the same types of pincer complexes. Herein the synthesis of a complete triad of Group 4 ‘pincer’ complexes is reviewed and their reaction chemistry demonstrating (a) nucleophilic alkylation, (b) the Lewis Acidity of the metal, (c) 1,2 addition across the MC carbene bond and (d) [2+2] cycloaddition across this MC bond is surveyed. The structural data for the ‘pincer’ complexes suggests strongly that there is a MC carbene double bond. The addition reactions also support this interpretation because a MC bond persists after the addition. The reactivity pattern also strongly suggests that the chemistry of this carbene center is similar to the metal alkylidene complexes, and not the Fischer heteroatom carbene complexes. The chemistry extends to many other elements. The extension to Sm as a representative lanthanide is described. This species adopts a structure very similar to the Group 4 ‘pincers’. Chromium(II) gave a novel bridging carbene dimer instead of the monomeric pincer. This bridging structure is developing as another structural motif in this system.

Reactions of Cationic Bridging Carbyne Complexes of Bis(η-cyclopentadienyl)diiron Tricarbonyl with Nucleophiles. A Route to Diiron Bridging Carbene Complexes

The reactions of the cationic carbyne complex of diiron, [Fe2(μ-CO)(μ-CPh)(CO)2(η-C5H5)2]BBr4 (3), with NaSMe, NaSEt, NaSPh, NaSC6H4Me-p, and NaSC6H4NO2-p in THF at low temperature afforded diiron bridging thiocarbene complexes [Fe2(μ-CO){μ-C(SR)Ph}(CO)2(η-C5H5)2] (5, R = Me; 6, R = Et; 7, R = Ph; 8, R = p-MeC6H4; 9, R = p-NO2C6H4). Complex [Fe2(μ-CO)(μ-CC6H4Me-p)(CO)2(η-C5H5)2]BBr4 (4) reacted similarly with NaSPh and NaSC6H4Me-p to give corresponding bridging carbene complexes [Fe2(μ-CO){μ-C(SR)C6H4Me-p}(CO)2-(η-C5H5)2] (10, R = Ph; 11, R = p-MeC6H4). Complex 3 also reacted with NaOPh and NaN(SiMe3)2 to yield bridging carbene complexes [Fe2(μ-CO){μ-C(OPh)Ph}(CO)2(η-C5H5)2] (12) and [Fe2(μ-CO){μ-C(N(SiMe3)2)Ph}(CO)2(η-C5H5)2] (13), respectively. Complexes 3 and 4 reacted with reactive salt [Et3NH][Fe2(μ-CO)(μ-SBun)(CO)6] to yield the bridging mercaptocarbene complex [Fe2(μ-CO){μ-C(SH)Ph}(CO)2(η-C5H5)2] (14) and the bridging butylthiocarbene complex [Fe2(μ-CO){μ-C(SBun)C6H4Me-p}(CO)2(η-C5H5)2] (15), respectively. The analogous reactions of [Et3NH][Fe2(μ-CO)(μ-SPh)(CO)6] with 3 and 4 afforded the thiolato-bridged iron carbonyl compound [Fe2(μ-SPh)2(CO)6] (16) and the bridging arylcarbene complexes [Fe2(μ-CO){μ-C(H)Ar}(CO)2(η-C5H5)2] (17, Ar = Ph; 18, Ar = p-MeC6H4), while [Et3NH][Fe2(μ-CO)(μ-SC6H4Me-p)(CO)6] reacted with 3 to yield 17 and [Fe2(μ-SC6H4Me-p)2(CO)6] (19). The reaction of metal carbonyl anion compounds Na2W(CO)5 and Na2Fe(CO)4 with 3 gave the same product, 17. The structures of 6, 7, 15, and 17 have been established by X-ray diffraction studies.

Solid state and solution structure of the hetero-dimetallic complexes [Cp(CO)2Re{μ-C(OMe)(Ph)}Pt(COD)] and [Cp(CO)2Re{μ-CPh}Pt(COD)]+, containing bridging carbene and carbyne ligands

The reaction of the carbene complex [Cp(CO)2Re=C(OMe)(Ph)] with [Pt(COD)2] affords in high yield the novel complex [Cp(CO)2Re{μ-C(OMe)(Ph)}Pt(COD)] (2), containing a bridging carbene ligand. Reaction of 2 with (Me3O)BF4 results in removal of the carbene-bound methoxy group, with formation of the cation [Cp(CO)2Re{μ-CPh}Pt(COD)]+ (3), in which a bridging carbyne is present. Both the complexes contain only ligands coordinated through carbon atoms and represent the highest members, as far as the Pt:Re ratio is concerned, of the small family of phosphorous-free Pt–Re mixed metal complexes containing Pt-Re bonds. Their full 1H and 13C NMR characterization in solution and their single-crystal solid state diffractometric analysis are reported and discussed. The X-ray analysis evidenced the substantially symmetric nature of the carbene bridge in the dimetalla-cyclopropane ring of complex 2 [Re-Pt 2.7188(3), Re-(μ-C) 2.166(4) and Pt-(μ-C) 2.055(4) Å]. In complex 3 the bond length pattern within the three-membered ring is suggestive of a significant double-bond character for the Re-(μ-C) interaction [Re-Pt 2.707(1), Re-(μ-C) 1.904(9) and Pt-(μ-C) 1.981(8) Å]. Both complexes show a semi-bridging CO ligand, with Pt⋯C distances of 2.452(4) and 2.299(9) Å, in 2 and 3, respectively. The 13C NMR characterization showed that the Pt⋯CO interaction is also maintained in solution in both complexes. In cation 3 a libration of the ReCp(CO)2 fragment around the Pt-Re axis, fast down to 193 K, interchanges the two carbonyl locations observed in the solid state, as well as the environments of couples of COD carbon atoms, leading to an apparent Cs symmetry. The correlation between spectroscopic data and structural features (concerning bridging carbenes or carbynes and semi-bridging carbonyls) in the class of heterodimetallic M–Pt complexes is discussed.