Bimetallic Reactivity of Dirhodium Compounds Leading to Functionalized Methylene-Bridged Compounds

C-Cl Bond Activation at Rotated vs Unrotated Dinuclear Site Related to [FeFe]-Hydrogenases

The novel dinuclear complex related to the [FeFe]-hydrogenases active site, [Fe2(μ-pdt)(κ2-dmpe)2(CO)2] (1), is highly reactive toward chlorinated compounds CHxCl4-x (x = 1, 2) affording selectively terminal or bridging chloro diiron isomers through a C-Cl bond activation. DFT calculations suggest a cooperative mechanism involving a formal concerted regioselective chloronium transfer depending on the unrotated or rotated conformation of two isomers of 1.

Methylene insertion into an Fe2S2 cluster: formation of a thiolate-bridged diiron complex containing an Fe-CH2-S moiety

Reduction of a thiolate-bridged FeIIFeIII complex leads to the cleavage of an Fe-S bond by the insertion of the methylene unit from CH2Cl2 to give a neutral FeIIFeIII complex with a novel Fe-CH2-S fragment. The structural and electrochemical differences of the alkylated and the non-alkylated Fe2S2 complexes are also examined.

The role of solvent in organometallic chemistry — Oxidative addition with dichloromethane or chloroform

Dimethylplatinum(II) complexes [PtMe2(NN)], with NN = diimine ligand, can react with dichloromethane or chloroform solvent to give the corresponding organoplatinum(IV) complexes [PtClMe2(CH2Cl)(NN)] or [PtClMe2(CHCl2)(NN)], respectively. The products can exist in isomeric forms, corresponding to products of cis or trans oxidative addition. The structures of three dichloromethane adducts and one chloroform adduct are reported.

Facile synthetic access to rhenium(II) complexes: activation of carbon-bromine bonds by single-electron transfer

The five-coordinated Re(I) hydride complexes [Re(Br)(H)(NO)(PR(3))(2)] (R=Cy 1 a, iPr 1 b) were reacted with benzylbromide, thereby affording the 17-electron mononuclear Re(II) hydride complexes [Re(Br)(2)(H)(NO)(PR(3))(2)] (R=Cy 3 a, iPr 3 b), which were characterized by EPR, cyclic voltammetry, and magnetic susceptibility measurements. In the case of dibromomethane or bromoform, the reaction of 1 afforded Re(II) hydrides 3 in addition to Re(I) carbene hydrides [Re(=CHR(1))(Br)(H)(NO)(PR(3))(2)] (R(1)=H 4, Br 5; R=Cy a, iPr b) in which the hydride ligand is positioned cis to the carbene ligand. For comparison, the dihydrogen Re(I) dibromide complexes [Re(Br)(2)(NO)(PR(3))(2)(eta(2)-H(2))] (R=Cy 2 a, iPr 2 b) were reacted with allyl- or benzylbromide, thereby affording the monophosphine Re(II) complex salts [R(3)PCH(2)R'][Re(Br)(4)(NO)(PR(3))] (R'=-CH=CH(2) 6, Ph 7). The reduction of Re(II) complexes has also been examined. Complex 3 a or 3 b can be reduced by zinc to afford 1 a or 1 b in high yield. Under catalytic conditions, this reaction enables homocoupling of benzylbromide (turnover frequency (TOF): 3 a 150, 3 b 134 h(-1)) or allylbromide (TOF: 3 a 575, 3 b 562 h(-1)). The reaction of 6 a and 6 b with zinc in acetonitrile affords in good yields the monophosphine Re(I) complexes [Re(Br)(2)(NO)(MeCN)(2)(PR(3))] (R=Cy 8 a, iPr 8 b), which showed high catalytic activity toward highly selective dehydrogenative silylation of styrenes (maximum TOF of 61 h(-1)). Single-electron transfer (SET) mechanisms were proposed for all these transformations. The molecular structures of 3 a, 6 a, 6 b, 7 a, 7 b, and 8 a were established by single-crystal X-ray diffraction studies.

Solvent-Dependent Interconversions between RhI, RhII, and RhIII Complexes of an Aryl–Monophosphine Ligand

Reaction of the aryl-monophosphine ligand alpha(2)-(diisopropylphosphino)isodurene (1) with the Rh(I) precursor [Rh(coe)(2)(acetone)(2)]BF(4) (coe=cyclooctene) in different solvents yielded complexes of all three common oxidation states of rhodium, depending on the solvent used. When the reaction was carried out in methanol a cyclometalated, solvent-stabilized Rh(III) alkyl-hydride complex (2) was obtained. However, when the reaction was carried out in acetone or dichloromethane a dinuclear eta(6)-arene Rh(II) complex (5) was obtained in the absence of added redox reagents. Moreover, when acetonitrile was added to a solution of either the Rh(II) or Rh(III) complexes, a new solvent-stabilized, noncyclometalated Rh(I) complex (6) was obtained. In this report we describe the different complexes, which were fully characterized, and probe the processes behind the remarkable solvent effect observed.

One-Electron versus Two-Electron Mechanisms in the Oxidative Addition Reactions of Chloroalkanes to Amido-Bridged Rhodium Complexes

The compound syn-[{Rh(mu-NH{p-tolyl})(CNtBu)(2)}(2)] (1) oxidatively adds C--Cl bonds of alkyl chlorides (RCl) and dichloromethane to each metal centre to give the cationic complexes syn-[{Rh(mu-NH{p-tolyl})(eta(1)-R)(CNtBu)(2)}(2)(mu-Cl)]Cl and anti-[{Rh(mu-NH{p-tolyl})Cl(CNtBu)(2)}(2)(mu-CH(2))]. Reaction of 1 with the chiral alkyl chloride (-)-(S)-ClCH(Me)CO(2)Me (R*Cl) gave [{Rh(mu-NH{p-tolyl})(eta(1)-R*)(CNtBu)(2)}(2)(mu-Cl)]Cl ([3]Cl) as an equimolecular mixture of the meso form (R,S)-[3]Cl-C(s) and one enantiomer of the chiral form [3]Cl-C(2). This reaction, which takes place in two steps, was modeled step-by-step by reacting the mixed-ligand complex syn-[(cod)Rh(mu-NH{p-tolyl})(2)Rh(CNtBu)(2)] (4) with R*Cl, as a replica of the first step, to give [(cod)Rh(mu-NH{p-tolyl})(2)RhCl(eta(1)-R*)(CNtBu)(2)] (5) with racemization of the chiral carbon. Further treatment of 5 with CNtBu to give the intermediate [(CNtBu)(2)Rh(mu-NH{p-tolyl})(2)RhCl(eta(1)-R*)(CNtBu)(2)], followed by reaction with R*Cl reproduced the regioselectivity of the second step to give (R,S)-[3]Cl-C(s) and [3]Cl-C(2) in a 1:1 molar ratio. Support for an S(N)2 type of reaction with inversion of the configuration in the second step was obtained from a similar sequence of reactions of 4 with ClCH(2)CO(2)Me first, then with CNtBu, and finally with R*Cl to give [(CNtBu)(2)(eta(1)-CH(2)R)Rh(mu-NH{p-tolyl})(2)(mu-Cl)Rh(eta(1)-R*)(CNtBu)(2)]Cl (R = CO(2)Me, [7]Cl) as a single enantiomer with the R configuration at the chiral carbon. The reactions of 1 with (+)-(S)-XCH(2)CH(CH(3))CH(2)CH(3) (X = Br, I) gave the related complexes [{Rh(mu-NH{p-tolyl})(eta(1)-CH(2)CH(CH(3))CH(2)CH(3))(CNtBu)(2)}(2)(mu-X)]X, probably by following an S(N)2 profile in both steps.

Unusual fragmentation of CH2Cl2by an Ir(iii) centre bonded to a doubly metalated TpMsLigand (TpMs= hydrotris(3-mesitylpyrazol-1-yl)borate)

The Ir(III) compound Tp(Ms'')Ir(N2), that contains a pentadentate, doubly metalated 3-mesityl substituted tris(pyrazolyl)borate ligand, induces the cleavage of C-H and C-Cl bonds of CH2Cl2 to yield a highly electrophilic chlorocarbene Ir=C(H)Cl complex.

Protonation reactions of dinuclear pyrazolato iridium(I) complexes

The complex [[Ir(mu-Pz)(CNBu(t))(2)](2)] (1) undergoes double protonation reactions with HCl and with HO(2)CCF(3) to give the neutral dihydride complexes [[Ir(mu-Pz)(H)(X)(CNBu(t))(2)](2)] (X = Cl, eta(1)-O(2)CCF(3)), in which the hydride ligands were located trans to the X groups and in the boat of the complexes, both in the solid state and in solution. The complex [[Ir(mu-Pz)(H)(Cl)(CNBu(t))(2)](2)] evolves in solution to the cationic complex [[Ir(mu-Pz)(H)(CNBu(t))(2)](2)(mu-Cl)]Cl. Removal of the anionic chloride by reaction with methyltriflate allows the isolation of the triflate salt [[Ir(mu-Pz)(H)(CNBu(t))(2)](2)(mu-Cl)]OTf. This complex undergoes a metathesis reaction of hydride by chloride in CDCl(3) under exposure to the direct sunlight to give the complex [[Ir(mu-Pz)(Cl)(CNBu(t))(2)](2)(mu-Cl)]OTf. Protonation of both metal centers in [[Ir(mu-Pz)(CO)(2)](2)] with HCl occurs at low temperature, but eventually the mononuclear compound [IrCl(HPz)(CO)(2)] is isolated. The related complex [[Ir(mu-Pz)(CO)(P[OPh](3))](2)] reacts with HCl and with HO(2)CCF(3) to give the neutral Ir(III)/Ir(III) complexes [[Ir(mu-Pz)(H)(X)(CO)(P[OPh](3))](2)], respectively. Both reactions were found to take place stepwise, allowing the isolation of the intermediate monohydrides. They are of different natures, i.e., the metal-metal-bonded Ir(II)/Ir(II) compound [(P[OPh](3))(CO)(Cl)Ir(mu-Pz)(2)Ir(H)(CO)(P[OPh](3))] and the mixed-valence Ir(I)/Ir(III) complex [(P[OPh](3))(CO)Ir(mu-Pz)(2)Ir(H)(eta(1)-O(2)CCF(3))(CO)(P[OPh](3))].

Stereoselective oxidative additions of iodoalkanes and activated alkynes to a sulfido-bridged heterotrinuclear early-late (TiIr2) complex

The reactions of the early-late trinuclear complex [Cp(acac)Ti(mu(3)-S)(2)Ir(2)(CO)(4)] (1) with electrophiles have been found to occur on the iridium atoms with no other involvement of the early metal than in electronic effects. The reaction with iodine gave two isomers of the diiridium(II) complex [Cp(acac)Ti(mu(3)-S)(2)Ir(2)I(2)(CO)(4)] differentiated by the relative positions of the iodo ligands on the iridium atoms. The reactions with iodoalkanes are highly stereoselective to give one sole isomer of formula [Cp(acac)Ti(mu(3)-S)(2)Ir(2)(R)(I)(CO)(4)] (R = CH(3), CH(2)I, CHI(2)) with a carbonyl and the iodo ligand trans to the metal-metal bond. The structures of the symmetrical isomer with the iodo ligands trans to the metal-metal bond and that of the compound with R = CHI(2) have been solved by X-ray diffraction methods. The stereoselectivity of the oxidative-addition reactions can be rationalized assuming the influence of steric effects of the groups on the titanium center and a radical-like mechanism. Reactions of 1 with the activated acetylenes, dimethylacetylenedicarboxylate and methylacetylenecarboxylate, gave the complexes [Cp(acac)Ti(mu(3)-S)(2)Ir(2)(mu-eta(1)-RC=CCO(2)Me)(CO)(4)] (R = CO(2)Me, H), with the alkyne bridging the two iridium centers as a cis-dimetalated olefin and the C=C bond parallel to the Ir-Ir axis. Two isomers resulting from the disposition of the alkyne along the Ir-Ir vector were observed in solution for the compound with the nonsymmetrical alkyne (R = H), while only one was observed for the compound with R = CO(2)Me. An exchange, fast in the NMR time scale, of the apical with the equatorial carbonyls occured in the complexes [Cp(acac)Ti(mu(3)-S)(2)Ir(2)(mu-eta(1)-RC=CCO(2)Me)(CO)(4)], producing their equivalence in the (13)C((1)H) NMR spectra.

Formation of nickel-thiolate aggregates via reaction with CH2Cl2

Reaction of the mononuclear nickel-thiolate complex [Ni(L1)(dppe)] with CH2Cl2 affords the novel pentanuclear complex [Ni5Cl2(L1)4(dppe)2], while [Ni(L1)(dcpe)] reacts with CH2Cl2 to give the binuclear species [Ni2Cl2(L2)(dcpe)2] in which two L1 units are linked by a methylene group derived from CH2Cl2.