Osazone anion radical complex of rhodium(III)

One electron paramagnetic parent osazone complex of rhodium of type trans-Rh(L(NHPh)H(2))(PPh(3))(2)Cl(2) (1), defined as an osazone anion radical complex of rhodium(III), trans-Rh(III)(L(NHPh)H(2)(?-))(PPh(3))(2)Cl(2), 1((t-RhL?)), with a minor contribution (～2%) of rhodium(II) electromer, trans-Rh(II)(L(NHPh)H(2))(PPh(3))(2)Cl(2), 1((t-Rh?L)), and their nonradical congener, trans-[Rh(III)(L(NHPh)H(2))(PPh(3))(2)Cl(2)]I(3) ([t-1](+)I(3)(-)), have been isolated and are substantiated by spectra, bond parameters, and DFT calculations on equivalent soft complexes [Rh(L(NHPh)H(2))(PMe(3))(2)Cl(2)] (3) and [Rh(L(NHPh)H(2))(PMe(3))(2)Cl(2)](+) (3(+)). 1 is not stable in solution and decomposes to [t-1](+) and a new rhodium(I) osazone complex, [Rh(I)(L(NHPh)H(2))(PPh(3))Cl] (2). 1 absorbs strongly at 351 nm due to MLCT and LLCT, while [t-1](+) and 2 absorb moderately in the range of 300-450 nm, respectively, due to LMCT and MLCT elucidated by TD-DFT calculations on 3((t-RhL?)), [t-3](+), and Rh(I)(L(NHPh)H(2))(PMe(3))Cl (4). EPR spectra of solids at 295 and 77 K, and dichloromethane-toluene frozen glass at 77 K of 1 are similar with g = 1.991, while g = 2.002 for the solid at 25 K. The EPR signal of 1 in dichloromethane solution is weaker (g = 1.992). In cyclic voltammetry, 1 displays two irreversible one electron transfer waves at +0.13 and -1.22 V, with respect to Fc(+)/Fc coupling, due to oxidation of 1((t-RhL?)) to [t-1](+) at the anode and reduction of rhodium(III) to rhodium(II), i.e., [t-1](+) to electromeric 1((t-Rh?L)) at the cathode.     

Gyroscope-like molecules consisting of three-spoke stators that enclose "switchable" neutral dipolar rhodium rotators; reversible cycling between faster and slower rotating Rh(CO)I and Rh(CO)2I species

trans-Rh(CO)(Cl)(P((CH(2))(14))(3)P) is prepared from trans-Rh(CO)(Cl)(P((CH(2))(6)CH[double bond, length as m-dash]CH(2))(3))(2) by a metathesis/hydrogenation sequence, and converted by substitution or addition reactions to Rh(CO)(I), Rh(CO)(2)(I), Rh(CO)(NCS), and Rh(CO)(Cl)(Br)(CCl(3)) species; the Rh(CO)(Cl) and Rh(CO)(I) moieties rapidly rotate within the cage-like diphosphine, but the other rhodium moieties do not.     

Transfer of amido groups from isolated rhodium(I) amides to alkenes and vinylarenes

The reaction of monomeric and dimeric rhodium(I) amido complexes with unactivated olefins to generate imines is reported. Transamination of {(PEt(3))(2)RhN(SiMePh(2))(2)} (1a) or its -N(SiMe(3))(2) analogue 1b with p-toluidine gave the dimeric [(PEt(3))(2)Rh(mu-NHAr)](2) (Ar = p-tolyl) (2a) in 80% isolated yield. Reaction of 2a with PEt(3) generated the monomeric (PEt(3))(3)Rh(NHAr) (Ar = p-tolyl) (3a). PEt(3)-ligated arylamides 2a and 3a reacted with styrene to transfer the amido group to the olefin and to form the ketimine Ph(Me)C=N(p-tol) (4a) in 48-95% yields. The dinuclear amido hydride (PEt(3))(4)Rh(2)(mu-NHAr)(mu-H) (Ar = p-tolyl) (5a) was formed from reaction of 2a in 95% yield, and a mixture of this dimeric species and the (PEt(3))(n)RhH complexes with n = 3 and 4 was formed from reaction of 3a in a combined 75% yield. Propene reacted with 2a to give Me(2)C=N(p-tol) (4b) and 5a in 90 and 57% yields. Propene also reacted with 3a to give 4b and 5a in 65 and 94% yields. Analogues of 2a and 3a with varied electronic properties also reacted with styrene to form the corresponding imines, and moderately faster rates were observed for reactions of electron-rich arylamides. Kinetic studies of the reaction of 3a with styrene were most consistent with formation of the imine by migratory insertion of olefin into the rhodium-amide bond to generate an aminoalkyl intermediate that undergoes beta-hydrogen elimination to generate a rhodium hydride and an enamine that tautomerizes to the imine.     

Synthesis, characterization, and reactivity of rhodium(I) acetylacetonato complexes containing pyridinecarboxaldimine ligands

Addition of o-C 6H 4NCHNAr to Rh(coe) 2(acac) (coe = cis-cyclooctene, acac = acetylacetonato) gave several new iminopyridine rhodium(I) complexes of the type Rh(acac)(kappa (2)- o-C 6H 4 NCH NAr) ( 1a Ar = 4-C 6H 4-OMe; 1b Ar = 2,6-C 6H 3-Me 2; 1c Ar = 2,6-C 6H 3-Et 2; 1d Ar = 2,6-C 6H 3- i-Pr 2). All new rhodium complexes have been characterized by a number of physical methods, including multinuclear NMR spectroscopy and X-ray diffraction studies for 1b and 1c. Addition of CHCl 3 to 1a afforded the corresponding rhodium(III) complex trans-Rh(kappa (2)- o-C 6H 4 NCH NAr)(CHCl 2)(Cl)(acac) ( 2). Addition of B 2cat 3 (cat = 1,2-O 2C 6H 4) to 1 gave zwitterionic Rh(eta (6)-catBcat)(kappa (2)- o-C 6H 4 NCH NAr) ( 3). The molecular structure of 3b has been confirmed by a single crystal X-ray diffraction study and shows that the N 2Rh fragment is bound to the catBcat anion via one of the catecholato groups in a eta (6)-fashion. These complexes have also been examined for their ability to catalyze the hydroboration of a series of vinylarenes. Reactions using catecholborane and pinacolborane seem to proceed largely through a dehydrogenative borylation mechanism to give a number of boronated products.     

The synthesis, characterisation and reactivity of 2-phosphanylethylcyclopentadienyl complexes of cobalt, rhodium and iridium

2-Phosphanylethylcyclopentadienyl lithium compounds, Li[C(5)R'(4)(CH(2))(2)PR(2)] (R = Et, R' = H or Me, R = Ph, R' = Me), have been prepared from the reaction of spirohydrocarbons C(5)R'(4)(C(2)H(4)) with LiPR(2). C(5)Et(4)HSiMe(2)CH(2)PMe(2), was prepared from reaction of Li[C(5)Et(4)] with Me(2)SiCl(2) followed by Me(2)PCH(2)Li. The lithium salts were reacted with [RhCl(CO)(2)](2), [IrCl(CO)(3)] or [Co(2)(CO)(8)] to give [M(C(5)R'(4)(CH(2))(2)PR(2))(CO)] (M = Rh, R = Et, R' = H or Me, R = Ph, R' = Me; M = Ir or Co, R = Et, R' = Me), which have been fully characterised, in many cases crystallographically as monomers with coordination of the phosphorus atom and the cyclopentadienyl ring. The values of nu(CO) for these complexes are usually lower than those for the analogous complexes without the bridge between the cyclopentadienyl ring and the phosphine, the exception being [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (Cp' = C(5)Me(4)), the most electron rich of the complexes. [Rh(C(5)Et(4)SiMe(2)CH(2)PMe(2))(CO)] may be a dimer. [Co(2)(CO)(8)] reacts with C(5)H(5)(CH(2))(2)PEt(2) or C(5)Et(4)HSiMe(2)CH(2)PMe(2) (L) to give binuclear complexes of the form [Co(2)(CO)(6)L(2)] with almost linear PCoCoP skeletons. [Rh(Cp'(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are active for methanol carbonylation at 150 degrees C and 27 bar CO, with the rate using [Rh(Cp'(CH(2))(2)PPh(2))(CO)] (0.81 mol dm(-3) h(-1)) being higher than that for [RhI(2)(CO)(2)](-) (0.64 mol dm(-3) h(-1)). The most electron rich complex, [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (0.38 mol dm(-3) h(-1)) gave a comparable rate to [Cp*Rh(PEt(3))(CO)] (0.30 mol dm(-3) h(-1)), which was unstable towards oxidation of the phosphine. [Rh(Cp'(CH(2))(2)PEt(2))I(2)], which is inactive for methanol carbonylation, was isolated after the methanol carbonylation reaction using [Rh(Cp'(CH(2))(2)PEt(2))(CO)]. Neither of [M(Cp'(CH(2))(2)PEt(2))(CO)] (M = Co or Ir) was active for methanol carbonylation under these conditions, nor under many other conditions investigated, except that [Ir(Cp'(CH(2))(2)PEt(2))(CO)] showed some activity at higher temperature (190 degrees C), probably as a result of degradation to [IrI(2)(CO)(2)](-). [M(Cp'(CH(2))(2)PEt(2))(CO)] react with MeI to give [M(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] (M = Co or Rh) or [Ir(Cp'(CH(2))(2)PEt(2))Me(CO)]I. The rates of oxidative addition of MeI to [Rh(C(5)H(4)(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are 62 and 1770 times faster than to [Cp*Rh(CO)(2)]. Methyl migration is slower, however. High pressure NMR studies show that [Co(Cp'(CH(2))(2)PEt(2))(CO)] and [Cp*Rh(PEt(3))(CO)] are unstable towards phosphine oxidation and/or quaternisation under methanol carbonylation conditions, but that [Rh(Cp'(CH(2))(2)PEt(2))(CO)] does not exhibit phosphine degradation, eventually producing inactive [Rh(Cp'(CH(2))(2)PEt(2))I(2)] at least under conditions of poor gas mixing. The observation of [Rh(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] under methanol carbonylation conditions suggests that the rhodium centre has become so electron rich that reductive elimination of ethanoyl iodide has become rate determining for methanol carbonylation. In addition to the high electron density at rhodium.     

Cationic rhodium mono-phosphine fragments partnered with carborane monoanions [closo-CB11H6X6]- (X = H, Br). Synthesis, structures and reactivity with alkenes

Addition of the new phosphonium carborane salts [HPR(3)][closo-CB(11)H(6)X(6)] (R = (i)Pr, Cy, Cyp; X = H 1a-c, X = Br 2a-c; Cy = C(6)H(11), Cyp = C(5)H(9)) to [Rh(nbd)(mu-OMe)](2) under a H(2) atmosphere gives the complexes Rh(PR(3))H(2)(closo-CB(11)H(12)) 3 (R = (i)Pr 3a, Cy 3b, Cyp 3c) and Rh(PR(3))H(2)(closo-CB(11)H(6)Br(6)) 4 (R = (i)Pr 4a, Cy 4b, Cyp 4c). These complexes have been characterised spectroscopically, and for 4b by single crystal X-ray crystallography. These data show that the {Rh(PR(3))H(2)}(+) fragment is interacting with the lower hemisphere of the [closo-CB(11)H(6)X(6)](-) anion on the NMR timescale, through three Rh-H-B or Rh-Br interactions for complexes 3 and 4 respectively. The metal fragment is fluxional over the lower surface of the cage anion, and mechanisms for this process are discussed. Complexes 3a-c are only stable under an atmosphere of H(2). Removing this, or placing under a vacuum, results in H(2) loss and the formation of the dimer species Rh(2)(PR(3))(2)(closo-CB(11)H(12))(2) 5a (R = (i)Pr), 5b (R = Cy), 5c (R = Cyp). These dimers have been characterised spectroscopically and for 5b by X-ray diffraction. The solid state structure shows a dimer with two closely associated carborane monoanions surrounding a [Rh(2)(PCy(3))(2)](2+) core. One carborane interacts with the metal core through three Rh-H-B bonds, while the other interacts through two Rh-H-B bonds and a direct Rh-B link. The electronic structure of this molecule is best described as having a dative Rh(I) --> Rh(III), d(8)--> d(6), interaction and a formal electron count of 16 and 18 electrons for the two rhodium centres respectively. Addition of H(2) to complexes 5a-c regenerate 3a-c. Addition of alkene (ethene or 1-hexene) to 5a-c or 3a-c results in dehydrogenative borylation, with 1, 2, and 3-B-vinyl substituted cages observed by ESI-MS: [closo-(RHC[double bond, length as m-dash]CH)(x)CB(11)H(12-x)](-)x = 1-3, R = H, C(4)H(9). Addition of H(2) to this mixture converts the B-vinyl groups to B-ethyl; while sequential addition of 4 cycles of ethene (excess) and H(2) to CH(2)Cl(2) solutions of 5a-c results in multiple substitution of the cage (as measured by ESI-MS), with an approximately Gaussian distribution between 3 and 9 substitutions. Compositionally pure material was not obtained. Complexes 4a-c do not lose H(2). Addition of tert-butylethene (tbe) to 4a gives the new complex Rh(P(i)Pr(3))(eta(2)-H(2)C=CH(t)Bu)(closo-CB(11)H(6)Br(6)) 6, characterised spectroscopically and by X-ray diffraction, which show coordination of the alkene ligand and bidentate coordination of the [closo-CB(11)H(6)Br(6)](-) anion. By contrast, addition of tbe to 4b or 4c results in transfer dehydrogenation to give the rhodium complexes Rh{PCy(2)(eta(2)-C(6)H(9))}(closo-CB(11)H(6)Br(6)) 7 and Rh{PCyp(2)(eta(2)-C(5)H(7))}(closo-CB(11)H(6)Br(6)) 9, which contain phosphine-alkene ligands. Complex has been characterised crystallographically.     

Highly bulky and electron-rich terminal ruthenium phosphido complexes: new donor ligands for palladium-catalyzed suzuki cross-couplings

Secondary phosphine complexes of the formula [(eta(5)-C(5)H(5))Ru(L)(2)(PHR(2))](+) BAr(F)(-) are prepared from cationic ruthenium N(2) complexes and PHR(2) (R = Ph (a), t-Bu (b), Cy (c)). Additions of t-BuOK or NaN(SiMe(3))(2) give the phosphido complexes (eta(5)-C(5)H(5))Ru(L)(2)(PR(2)) ((L)(2) = (PEt(3))(2) (5a-c), depe (6a,b)) in high NMR yields. These rapidly oxidize in air to give isolable RuP(=O)R(2) species. Complex 5a is more basic than the rhenium analogue (eta(5)-C(5)H(5))Re(NO)(PPh(3))(PPh(2)), and 6b is more basic than P-t-Bu(3). Complexes 5a-c and 6b are effective ligands for palladium-catalyzed Suzuki reactions. The catalyst from 6b is nearly as reactive as that from the benchmark ligand P-t-Bu(3).     

C-F or C-H bond activation and C-C coupling reactions of fluorinated pyridines at rhodium: synthesis, structure and reactivity of a variety of tetrafluoropyridyl complexes

Reactions of [RhH(PEt3)3] (1) or [RhH(PEt3)4] (2) with pentafluoropyridine or 2,3,5,6-tetrafluoropyridine afford the activation product [Rh(4-C5NF4)(PEt3)3] (3). Treatment of 3 with CO, 13CO or CNtBu effects the formation of trans-[Rh(4-C5NF4)(CO)(PEt3)2] (4a), trans-[Rh(4-C5NF4)(13CO)(PEt3)2] (4b) and trans-[Rh(4-C5NF4)(CNtBu)(PEt3)2] (5). The rhodium(III) compounds trans-[RhI(CH3)(4-C5NF4)(PEt3)2] (6a) and trans-[RhI(13CH3)(4-C5NF4)(PEt3)2] (6b) are accessible on reaction of 3 with CH3I or 13CH3I. In the presence of CO or 13CO these complexes convert into trans-[RhI(CH3)(4-C5NF4)(CO)(PEt3)2] (7a), trans-[RhI(13CH3)(4-C5NF4)(CO)(PEt3)2] (7b) and trans-[RhI(13CH3)(4-C5NF4)(13CO)(PEt3)2] (7c). The trans arrangement of the carbonyl and methyl ligand in 7a-7c has been confirmed by the 13C-13C coupling constant in the 13C NMR spectrum of 7c. A reaction of 4a or 4b with CH3I or 13CH3I yields the acyl compounds trans-[RhI(COCH3)(4-C5NF4)(PEt3)2] (8a) and trans-[RhI(13CO13CH3)(4-C5NF4)(PEt3)2] (8b), respectively. Complex 8a slowly reacts with more CH3I to give [PEt3Me][Rh(I)2(COCH3)(4-C5NF4)(PEt3)](9). On heating a solution of 7a, the complex trans-[RhI(CO)(PEt3)2] (10) and the C-C coupled product 4-methyltetrafluoropyridine (11) have been obtained. Complex 8a also forms 10 at elevated temperatures in the presence of CO together with the new ketone 4-acetyltetrafluoropyridine (12). The structures of the complexes 3, 4a, 5, 6a, 8a and 9 have been determined by X-ray crystallography. 19F-1H HMQC NMR solution spectra of 6a and 8a reveal a close contact of the methyl groups in the phosphine to the methyl or acyl ligand bound at rhodium.     

Reactivity of novel N,N'-diphosphino-silanediamine-based rhodium(I) derivatives

The coordination abilities of the novel N,N'-diphosphino-silanediamine ligand of formula SiMe(2)(NtolPPh(2))(2) (SiNP, 1) have been investigated toward rhodium, and the derivatives [RhCl(SiNP)](2) (2), [Rh(SiNP)(COD)][BF(4)] (3), and Rh(acac)(SiNP) (4) have been synthesized. The stability of the dinuclear frame of [RhCl(SiNP)](2) (2) toward incoming nucleophiles has been shown to be dependent on their π-acceptor ability. Indeed, the mononuclear complexes RhCl(SiNP)(L) (L = CO, 5; CN(t)Bu, 6) have been isolated purely and quantitatively upon reaction of 2 with CO and CN(t)Bu, respectively. Otherwise, PPh(3) and RhCl(SiNP) equilibrate with Rh(Cl)(SiNP)(PPh(3)) (7). Carbon electrophiles such as MeI and 3-chloro-1-proprene afforded the oxidation of rhodium(I) to rhodium(III) and the formation of RhCl(2)(η(3)-C(3)H(5))(SiNP) (8) and Rh(Me)(I)(SiNP)(acac) (10), respectively. The methyl derivative 10 is thermally stable and does not react either with CO or with CN(t)Bu even in excess. Otherwise, RhCl(2)(η(3)-C(3)H(5))(SiNP) (8) is thermally stable but reacts with CO, affording 3-chloro-1-proprene and RhCl(SiNP)(CO) (5). Finally, upon reaction of Rh(acac)(SiNP) (4) and 3-chloro-1-proprene, RhCl(acac)(η(1)-C(3)H(5))(SiNP) (9a) and [Rh(acac)(η(3)-C(3)H(5))(SiNP)]Cl (9b) could be detected at 233 K. At higher temperatures, 9a and 9b smoothly decompose, affording the dinuclear derivative [RhCl(SiNP)](2) (2) and the CC coupling product 3-allylpentane-2,4-dione.     

Substitution and hydrogenation reactions on rhodium(I)-ethylene complexes of the hydrotris(pyrazolyl)borate ligands T (T = Tp, TpMe2)

The bis(ethylene) Rh species TpMe2Rh(C2H4)2(1*) (TpMe2 = tris(3,5-dimethyl-1-pyrazol-1-yl)hydroborate) has been obtained from [RhCl(C2H4)2]2 and KTpMe2. Complex 1* easily decomposes in solution to give mainly the butadiene species TpMe2Rh(eta74-C4H6). In the solid state its thermal decomposition follows a different course and the allyl TpMe2RhH(syn-C3H4Me) is cleanly obtained as a mixture of exo and endo isomers. The complexes Tp'Rh(C2H4)2 (Tp' = Tp, TpMe2) afford the monosubstituted species Tp'Rh(C2H4)(PR3) upon reaction with PR3 but react differently with L = CO or CNR: the Tp compound gives dinuclear [TpRh]2(mu-L)3 complexes, while, in the case of 1*, TpMe2Rh(C2H4)(L) species are obtained. The ethylene ligand of complexes TpMe2Rh(C2H4)(PR3) is labile, and several peroxo compounds of composition TpMe2Rh(O2)(PR3) have been isolated by their reaction with O2. All the mononuclear Rh(I) complexes are formulated as 18e- trigonal bipyramidal species on the basis of IR and NMR spectroscopic studies. A series of dihydride complexes of Rh(III) of formulation Tp'RhH2(PR3) have been prepared by the hydrogenation of the corresponding ethylene derivatives. Complexes [TpRh]2(mu-CNCy)3, TpMe2Rh(C2H4)(PEt3), and TpMe2Rh(O2)(PEt3) have been further characterized by X-ray diffraction studies.     

The influence of phosphane coligands on the nuclearity of rhodium(I) 4-thiolatobenzoic acid complexes

[RhCl(PR3)3] (R = Ph, Et) reacts with the potassium salt of 4-mercaptobenzoic acid to give a mixture of the monomeric and dimeric complexes, [Rh(SC6H4COOH)(PR3)3] and [{Rh(-SC6H4COOH)(PR3)2}2], respectively. With the labile PPh3 coligand, the dimer is the major product, while for the electron-richer coligand PEt3, the equilibrium is easily shifted to the monomer by the addition of excess PEt3. Phosphane dissociation and dimerization could be prevented by using the chelating coligand PPh(C2H4PPh2)2. [{Rh(-SC6H4COOH)(PPh3)2}2] (2b), [Rh(SC6H4COOH)(PEt3)3] (3a), and [Rh(SC6H4COOH){PPh(C2H4PPh2)2}] (4) were fully characterized by nuclear magnetic resonance and infrared spectroscopy, mass spectrometry, and elemental analysis. The molecular structures of 2b and 4 were determined by X-ray structure analysis. In solution, the lability of the phosphane ligands leads to the decomposition of 2b. One of the decomposition products, namely, the mixed-valent complex [{RhIRhIII(-SC6H4COO)(-SC6H4COOH)(SC6H4COOH)(PPh3)3}2] (5), was characterized by X-ray structural analysis. The dinuclear rhodium(III) complex [{Rh(-SC6H4COO)(SC6H4COOH)(PEt3)2}2] (6) was shown to be a byproduct in the synthesis of 3a, and this demonstrates the reactivity of the rhodium(I) complexes toward oxidative addition. The structurally characterized complexes 2b, 4, 5, and 6 show hydrogen bonding of the free carboxyl groups.     

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))].     

Oxygen reduction to water mediated by a dirhodium hydrido-chloride complex

The two-electron mixed-valence dirhodium complex Rh(2)(0,II)(tfepma)(2)(CN(t)Bu)(2)Cl(2) (tfepma = CH(3)N[P(OCH(2)CF(3))(2)](2)) reacts with HCl to furnish two isomeric dirhodium hydrido-chloride complexes, Rh(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(3)H. In the presence of HCl, the hydride complex effects the reduction of 0.5 equiv of O(2) to 1 equiv of H(2)O, generating Rh(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(4), which can be prepared independently by chlorine oxidation of the Rh(2)(0,II) precursor. The starting Rh(2)(0,II) complex is regenerated photochemically to close an oxygen-to-water reduction photocycle.     

Dinickel(II) complexes: preparation and catalytic activity

Ligands (L(a-c)) based on 2,7-bis(3,5-di-R-pyrazol-1-yl)-1,8-naphthyridine (a, R = H; b, R = CH(3); c, R = Ph) were prepared for the construction of a series of dinickel complexes. Treatment of L(x) with NiCl(2) in an anhydrous methanol/THF solution resulted in the formation of dinuclear complexes [(L(x))(μ-Cl)(2)Ni(2)Cl(2)(CH(3)OH)(2)] (3, x = a; 4, x = b; 5, x = c). These new complexes were characterized by elemental analysis, IR and UV-Vis spectroscopic techniques. The structures of complexes 3 and 4 were further confirmed by X-ray diffraction studies. Interestingly, crystals of 4 were obtained as a co-crystallization of 4 and the methanol substituted species [{(L(b))(μ-Cl)(2)Ni(2)Cl(CH(3)OH)(3)}Cl] (4'). These dinickel complexes have been tested in the catalytic homo-coupling of terminal alkynes with the use O(2) as the oxidant, showing excellent activities. A clear improvement on the catalytic activity of these complexes is observed as compared to the mono-nuclear species.     

Hydrodefluorination of pentafluoropyridine at rhodium using dihydrogen: detection of unusual rhodium hydrido complexes

The pentafluoropyridyl complex [Rh(4-C5NF4)(PEt3)3] (3) reacts with H2 to give initially the dihydrido complex cis-mer-[Rh(H)2(4-C5NF4)(PEt3)3] (6). Within a few hours 2,3,5,6-tetrafluoropyridine as well as two rhodium(III) complexes mer-[Rh(H)3(PEt3)3] (mer-) and fac-[Rh(H)3(PEt3)3] (fac-) are formed. A catalytic C-F activation process for the formation of 2,3,5,6-tetrafluoropyridine starting from pentafluoropyridine and dihydrogen using 3 as a catalyst has been developed. Reaction of [RhH(PEt3)3] (1) with hydrogen affords fac-[Rh(H)3(PEt3)3] (fac-7) and mer-[Rh(H)3(PEt3)3] (mer-7) in a ratio of 1 : 7.25 at 193 K. The latter complex represents the first mononuclear rhodium compound bearing trans-hydrides.     

Mechanistic studies of O2 reduction effected by group 9 bimetallic hydride complexes

Synthetic and kinetic studies are used to uncover mechanistic details of the reduction of O(2) to water mediated by dirhodium complexes. The mixed-valence Rh(2)(0,II)(tfepma)(2)(CN(t)Bu)(2)Cl(2) (1, tfepma = MeN[P(OCH(2)CF(3))(2)](2), CN(t)Bu = tert-butyl isocyanide) complex is protonated by HCl to produce Rh(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(3)H (2), which promotes the reduction of O(2) to water with concomitant formation of Rh(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(4) (3). Reactions of the analogous diiridium complexes permit the identification of plausible reaction intermediates. Ir(2)(0,II)(tfepma)(2)(CN(t)Bu)(2)Cl(2) (4) can be protonated to form the isolable complex Ir(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(3)H (5), which reacts with O(2) to form Ir(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(3)(OOH) (6). In addition, 4 reacts with O(2) to form Ir(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(2)(η(2)-O(2)) (7), which can be protonated by HCl to furnish 6. Complexes 6 and 7 were both isolated in pure form and structurally and spectroscopically characterized. Kinetics examination of hydride complex 5 with O(2) and HCl furnishes a rate law that is consistent with an HCl-elimination mechanism, where O(2) binds an Ir(0) center to furnish an intermediate η(2)-peroxide intermediate. Dirhodium congener 2 obeys a rate law that not only is also consistent with an analogous HCl-elimination mechanism but also includes terms indicative of direct O(2) insertion and a unimolecular isomerization prior to oxygenation. The combined synthetic and mechanistic studies bespeak to the importance of peroxide and hydroperoxide intermediates in the reduction of O(2) to water by dirhodium hydride complexes.     

Preparation of a family of hexanuclear rhenium cluster complexes containing 5-(phenyl)tetrazol-2-yl ligands and alkylation of 5-substituted tetrazolate ligands

The preparation of two new families of hexanuclear rhenium cluster complexes containing benzonitrile and phenyl-substituted tetrazolate ligands is described. Specifically, we report the preparation of a series of cluster complexes with the formula [Re(6)Se(8)(PEt(3))(5)L](2+) where L = benzonitrile, p-aminobenzonitrile, p-methoxybenzonitrile, p-acetylbenzonitrile, or p-nitrobenzonitrile. All of these complexes undergo a [2 + 3] cycloaddition with N(3)(-) to generate the corresponding [Re(6)Se(8)(PEt(3))(5)(5-(p-X-phenyl)tetrazol-2-yl)](+) (or [Re(6)Se(8)(PEt(3))(5)(2,5-p-X-phenyltetrazolate)](+)) cluster complexes, where X = NH(2), OMe, H, COCH(3), or NO(2). Crystal structure data are reported for three compounds: [Re(6)Se(8)(PEt(3))(5)(p-acetylbenzonitrile)](BF(4))(2)?MeCN, [Re(6)Se(8)(PEt(3))(5)(2,5-phenyltetrazolate)](BF(4))?CH(2)Cl(2), and [Re(6)Se(8)(PEt(3))(5)(2,5-p-aminophenyltetrazolate)](BF(4)). Treatment of [Re(6)Se(8)(PEt(3))(5)(2,5-phenyltetrazolate)](BF(4)) with HBF(4) in CD(3)CN at 100 °C leads to protonation of the tetrazolate ring and formation of [Re(6)Se(8)(PEt(3))(5)(CD(3)CN)](2+). Surprisingly, alkylation of the phenyl and methyl tetrazolate complexes ([Re(6)Se(8)(PEt(3))(5)(2,5-N(4)CPh)](BF(4)) and [Re(6)Se(8)(PEt(3))(5)(1,5-N(4)CMe)](BF(4))) with methyl iodide and benzyl bromide, leads to the formation of mixtures of 1,5- and 2,5-disubstituted tetrazoles.     

In situ NMR observation of mono- and binuclear rhodium dihydride complexes using parahydrogen-induced polarization

Starting from the binuclear complex [RhCl(NBD)]2 (NBD = 2,5-norbornadiene) in the presence of the phosphines L = PMe3, PMe2Ph, PMePh2, PEt3, PEt2Ph, PEtPh2, or P(n-butyl)3, various mononuclear dihydrides of the type Rh(H)2CIL3, i.e., those of the homogeneous hydrogenation catalysts RhCIL3, have been obtained upon addition of parahydrogen, and their 1H NMR spectra have been investigated using parahydrogen-induced polarization (PHIP). Furthermore, the two binuclear complexes (H)(Cl)Rh(PMe3)2(mu-Cl)(mu-H)Rh(PMe3) and (H)(Cl)Rh(PMe2Ph)2(mu-Cl)(mu-H)Rh(PMe2Ph) have been detected and characterized by means of this in situ NMR method. Analogous complexes with trifluoroacetate instead of chloride, i.e., Rh(H)2(CF3COO)L3, have been generated in situ starting from Rh(NBD)(acac) in the presence of trifluoroacetic acid in combination with the phosphines L = PPh3, PEt2Ph, PEt3, and P(n-butyl)3, and their 1H NMR parameters have been determined.     

Unprecedented chemical transformation of semicarbazones mediated by Wilkinson's catalyst

para-Nitrobenzaldehyde semicarbazone undergoes an unusual chemical transformation upon reaction with [Rh(PPh(3))(3)Cl] in the presence of trialkyl and dialkylamines (NR(2)R'; R = Et,(i)Pr, (n)Bu; R' = H or R' = R) via dissociation of the C-NH(2) bond and formation of a new C-NR(2) bond (where the NR(2) fragment is provided by the amine). The transformed semicarbazone ligand binds to rhodium as a dianionic C,N,O-donor to afford complexes of type [Rh(PPh(3))(2)(CNO-NR(2))Cl] (CNO-NR(2) = the coordinated semicarbazone ligand). Another group of semicarbazones (viz. salicylaldehyde semicarbazone, 2-hydroxyacetophenone semicarbazone, and 2-hydroxynaphthaldehyde semicarbazone) has also been observed to undergo a similar chemical transformation upon reaction with [Rh(PPh(3))(3)Cl] under similar experimental conditions as before, and these transformed semicarbazones bind to rhodium as dianionic O,N,O-donors affording complexes of the type [Rh(PPh(3))(2)(ONO(n)-NR(2))Cl] (ONO(n)-NR(2) = the coordinated semicarbazone ligand; n = 1-3). The structure of the [Rh(PPh(3))(2)(CNO-NEt(2))Cl] and [Rh(PPh(3))(2)(ONO(2)-NR(2))Cl] complexes has been determined. All the complexes show characteristic (1)H NMR signals. They also show intense absorptions in the visible and ultraviolet region. Cyclic voltammetry on the complexes shows an oxidative response within 0.52-0.97 V versus SCE and a reductive response within -1.00 to -1.27 V versus SCE, where both the responses are believed to be centered on the semicarbazone ligand.     

Rhodium(I) and rhodium(III) complexes formed by coordination and C-H activation of bulky functionalized phosphanes

The reaction of [[RhCl(C(8)H(14))(2)](2)] (2) with iPr(2)PCH(2)CH(2)C(6)H(5) (L(1)) led, via the isolated dimer [[RhCl(C(8)H(14))(L(1))](2)] (3), to a mixture of three products 4 a-c, of which the dinuclear complex [[RhCl(L(1))(2)](2)] (4 a) was characterized by Xray crystallography. The mixture of 4a-c reacts with CO, ethene, and phenylacetylene to give the square-planar compounds trans-[RhCl(L)(L(1))(2)] (L=CO (5), C(2)H(4) (6), C=CHPh (9)). The corresponding allenylidene(chloro) complex trans-[RhCl(=C=C=CPh(2))(L(1))(2)] (11), obtained from 4 a-c and HC triple bond CC(OH)Ph(2) via trans-[RhCl[=C=CHC(OH)Ph(2)](L(1))(2)] (10), could be converted stepwise to the related hydroxo, cationic aqua, and cationic acetone derivatives 12-14, respectively. Treatment of 2 and [[RhCl(C(2)H(4))(2)](2)] (7) with two equivalents of tBu(2)PCH(2)CH(2)C(6)H(5) (L(2)) gave the dimers [[RhCl(C(8)H(14))(L(2))](2)] (15) and [[RhCl(C(2)H(4))(L(2))](2)] (16), which both react with L(2) in the molar ratio of 1:2 to afford the five-coordinate aryl(hydrido)rhodium(III) complex [RhHCl(C(6)H(4)CH(2)CH(2)PtBu(2)-kappa(2)C,P)(L(2))] (17) by C-H activation. The course of the reactions of 17 with CO, H(2), PhC triple bond CH, HCl, and AgPF(6), leading to the compounds 19-21, 24, and 25 a, respectively, indicate that the coordinatively unsaturated isomer of 17 with the supposed composition [RhCl(L(2))(2)] is the reactive species. Labeling experiments using D(2), DCl, and PhC triple bond CD support this proposal. With either [Rh(C(8)H(14))(eta(6)-L(2)-kappaP]PF(6) or [Rh(C(2)H(4))(eta(6)-L(n)-kappaP]PF(6) (n=1 and 2) as the starting materials, the corresponding halfsandwich-type complexes 27, 28, and 32 were obtained. The nonchelating counterpart of the dihydrido compound 32 with the composition [RhH(2)(PiPr(3))(eta(6)-C(6)H(6))]PF(6) (35) was prepared stepwise from [Rh(C(2)H(4))(PiPr(3))(eta(6)-C(6)H(6))]PF(6) and H(2) in acetone via the tris(solvato) species [RhH(2)(PiPr(3))(acetone)(3)]PF(6) (34) as intermediate. The synthesis of the bis(chelate) complex [Rh(eta(4)-C(8)H(12))(C(6)H(5)OCH(2)CH(2)PtBu(2)-kappa(2)O,P)]BF(4) (39) is also described. Besides 4 a, the compounds 17, 25 a, and 39 have been characterized by Xray crystal structure analysis.