Nickel(II)-catalyzed highly enantioselective hydrophosphination of methacrylonitrile

The dicationic Ni(II) complex [Ni(Pigiphos)(THF)](ClO4)2, [1](ClO4)2 ((R)-(S)-Pigiphos = bis-{(R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyl}cyclohexylphosphine), catalyzes the addition of bulky aliphatic secondary phosphines to methaacrylonitrile. This hydrophosphination reaction reaches TON = 900 and enantioselectivities up to 94%. A catalytic cycle involving 1,4-conjugate addition of R2PH to methacrylonitrile is supported by the isolation and characterization of a catalytically active N-coordinated, methacrylonitrile Ni complex.     

Boron and aluminum complexes of sterically demanding phosphinimines and phosphinimides

Reactions of sterically demanding phosphinimines R3PNH [R=i-Pr (1), t-Bu (2)] were examined. Reactions with B(C6F5)3 formed the adducts (R3PNH)B(C6F5)3 [R=i-Pr (3), t-Bu (4)] in high yield. On the other hand, 2 reacts with HB(OBu)2, evolving H2 to give t-Bu3PNB(OBu)2 (5). The reaction of 2 equiv of 2 with BH3.SMe2 affords the species (t-Bu3PN)2BH (6). In contrast, the reaction of n-Bu(t-Bu)2PNH with BH3.SMe2 results in the formation of the robust adduct n-Bu(t-Bu)2PNH.BH3 (8). An alternative route to borane-phosphinimide complexes involves Me3SiCl elimination, as exemplified by the reaction of BCl2Ph with n-Bu3PNSiMe3, which gives the product n-Bu3PNBCl(Ph) (9). The corresponding reactions of the parent phosphinimines 1 and 2 with AlH3.NMe2Et give the dimers [(mu-i-Pr3PN)AlH2]2 (10) and [(mu-t-Bu3PN)AlH2]2 (11). Species 11 reacts further with Me3SiO3SCF3 to provide [(mu-t-Bu3PN)AlH(OSO2CF3)]2 (12). The reaction of the lithium salt [t-Bu3PNLi]4 (13) with BCl3 proceeds smoothly to give t-Bu3PNBCl2 (14), which is readily alkylated to give t-Bu3PNBMe2 (15). Subsequent reaction of 15 with B(C6F5)3 results in methyl abstraction and the formation of [(mu-t-Bu3PN)BMe]2[MeB(C6F5)3]2 (16). The reaction of 13 in a 2:1 ratio with BCl3 gives the salt [(t-Bu3PN)2B]Cl (17). This species can be methylated to give (t-Bu3PN)2BMe (18), which undergoes subsequent reaction with [Ph3C][X] (X=[B(C6F5)4], [PF6]) to form the related salts [(t-Bu3PN)2B][B(C6F5)4] (19) and [(t-Bu3PN)2B][PF6] (20), respectively. Analogous reactions with [Ph3C][BF4] afforded [t-Bu3PNBF2]2 (21). Compounds 3, 4, 6, 8, 11, 12, 17, 19, and 21 were characterized by X-ray crystallography.     

A cycle for organic nitrile synthesis via dinitrogen cleavage

In the presence of NaH, the reaction between N2 and Mo(N[t-Bu]Ar)3 (Ar = 3,5-C6H3Me2) proceeds at room temperature to afford NMo(N[t-Bu]Ar)3 (95%). Lewis acidic silyl triflates (Me3SiOTf + pyridine or (i-Pr)3SiOTf) mediate a reaction between acid chlorides and NMo(N[t-Bu]Ar)3 to yield acyl imidos [RC(O)NMo(N[t-Bu]Ar)3][OTf] (R = Me, 92%; Ph, 75%; t-Bu, 64%). The reduction of [RC(O)NMo(N[t-Bu]Ar)3][OTf] by magnesium anthracene followed by treatment with Me3SiOTf affords molybdenum ketimides, R(Me3SiO)CNMo(N[t-Bu]Ar)3 (R = Me, 82%; Ph, 77%; t-Bu, 46%). Exposing R(Me3SiO)CNMo(N[t-Bu]Ar)3 to SnCl2 or ZnCl2 produces ClMo(N[t-Bu]Ar)3 (71-93% for SnCl2) and RCN (97-99%). Magnesium metal reduces ClMo(N[t-Bu]Ar)3 to Mo(N[t-Bu]Ar)3 (74%), completing a synthetic cycle. New strategies for the functionalization of sterically hindered nitrides and nitrile extrusion from d2 ketimides are presented in the context of a new route for derivatizing N2.     

Kinetics and mechanism of bromate-bromide reaction catalyzed by acetate

The initial rate of the bromate-bromide reaction, BrO3- + 5Br- + 6H+ --> 3Br2 + 3H2O, has been measured at constant ionic strength, I = 3.0 mol L(-1), and at several initial concentrations of acetate, bromate, bromide, and perchloric acid. The reaction was followed at the Br2/Br3- isosbestic point (lambda = 446 nm) by the stopped-flow technique. A very complex behavior was found such that the results could be fitted only by a six term rate law, nu = k1[BrO3-][Br-][H+]2 + k2[BrO3-][Br-]2[H+]2 + k3[BrO3-][H+]2[acetate]2 + k4[BrO3-][Br-]2[H+]2[acetate] + k5[BrO3-][Br-][H+]3[acetate]2 + k6[BrO3-][Br-][H+]2[acetate], where k1 = 4.12 L3 mol(-3) s(-1), k2 = 0.810 L4 mol(-4) s(-1), k3 = 2.80 x 10(3) L4 mol(-4) s(-1), k4 = 278 L5 mol(-5) s(-1), k5 = 5.45 x 10(7) L6 mol(-6) s(-1), and k6 = 850 L4 mol(-4) s(-1). A mechanism, based on elementary steps, is proposed to explain each term of the rate law. This mechanism considers that when acetate binds to bromate it facilitates its second protonation.     

Methylcyclopentadienyl-substituted tungsten(IV) sulfido cluster [(eta5-Cp')3W3S4]+ and its heterobimetallic derivative [(eta5-Cp')3W3S4Ni(PPh3)]+

The aqueous cluster salt [(H2O)9W3S4][pts]4.9H2O (pts = p-toluenesulfonate) was converted to the methylcyclopentadienyl (Cp') substituted cluster [(eta5-Cp')3W3S4][pts] ([1][pts]) from which the cubane-like cluster [(eta5-Cp')3W3S4Ni(PPh3)][pts] ([2][pts]) was obtained by reaction with Ni(cod)2 and PPh3. [2][pts] was characterized by X-ray crystal structure analysis.     

Proton transfer to nickel-thiolate complexes. 2. Rate-limiting intramolecular proton transfer in the reactions of [Ni(SC(6)H(4)R-4)(PhP[CH(2)CH(2)PPh(2)](2))](+) (R = NO(2), Cl, H, Me, or MeO)

The protonation of [Ni(SC(6)H(4)R-4)(triphos)](+) (triphos = PhP[CH(2)CH(2)PPh(2)](2); R = NO(2), Cl, H, Me, or MeO) by [lutH](+) (lut = 2,6-dimethylpyridine) to form [Ni(S(H)C(6)H(4)R-4)(triphos)](2+) is an equilibrium reaction in MeCN. Kinetic studies, using stopped-flow spectrophotometry, reveal that the reactions occur by a two-step mechanism. Initially, [lutH](+) rapidly binds to the complex (K(2)(R)) in an interaction which probably involves hydrogen-bonding of the acid to the sulfur. Subsequent intramolecular proton transfer from [lutH](+) to sulfur (k(3)(R)) is slow because of both electronic and steric factors. The X-ray crystal structures of [Ni(SC(6)H(4)R-4)(triphos)](+) (R = NO(2), H, Me, or MeO) show that all are best described as square-planar complexes, with the phenyl substituents of the triphos ligand presenting an appreciable barrier to the approach of the sterically demanding [lutH](+) to the sulfur. The kinetic characteristics of the intramolecular proton transfer from [lutH](+) to sulfur have been investigated. The rate of intramolecular proton transfer exhibits a nonlinear dependence on Hammett sigma(+), with both electron-releasing and electron-withdrawing 4-R-substituents on the coordinated thiolate facilitating the rate of proton transfer (NO(2) > Cl > H > Me < MeO). The rate constants for intramolecular proton transfer correlate well with the calculated electron density of the sulfur. The temperature dependence of the rate of the intramolecular proton transfer reactions shows that deltaH() is small but increases as the 4-R-substituent becomes more electron-withdrawing [deltaH = 4.1 (MeO), 6.9 (Me), 11.4 kcal mol(-)(1) (NO(2))], while DeltaS() becomes progressively less negative [deltaS = -50.1 (MeO), -41.2 (Me), -16.4 (NO(2)) cal K(-)(1) mol(-)(1)]. Studies with [lutD](+) show that the rate of intramolecular proton transfer varies with the 4-R-substituent [(k(3)(NO)2)(H)/(k(3)(NO)2)(D) = 0.39; (k(3)(Cl))(H)/(k(3)(Cl))(D) = 0.88; (k(3)(Me))(H)/(k(3)(Me))(D) = 1.3; (k(3)(MeO))(H)/(k(3)(MeO))(D) = 1.2].     

Chiral conducting salts of nickel dithiolene complexes

Conducting and chiral [Ni(dmit)(2)] dithiolene salts were obtained by electrocrystallization of the radical [n-Bu(4)N][Ni(dmit)(2)] salt in the presence of chiral, enantiopure trimethylammonium cations. Three different cations were investigated, namely, (R)-Ph(Me)HC*-NMe(3)(+), (S)-((t)Bu)(Me)HC*-NMe(3)(+), and (S)-(1-Napht)MeHC*-NMe(3)(+), noted (R)-1, (S)-2, and (S)-3. Salts of 1:3 stoichiometry were obtained with (R)-1 and (S)-2, formulated as [(R)-1][Ni(dmit)(2)](3) and [(S)-2][Ni(dmit)(2)](3)·(CH(3)CN)(2). They both crystallize in the P2(1)2(1)2(1) chiral space group, with three crystallographically independent complexes exhibiting different oxidation degrees. Another salt with 2:5 stoichiometry was isolated with (S)-3. The semiconducting character of the three salts (σ(RT) = 20-30 × 10(-3) S cm(-1)) finds its origin in a strong electron localization, favored by the large number of crystallographically independent [Ni(dmit)(2)] complexes in these chiral structures and their association into weakly interacting dimeric or trimeric motifs. Racemic salts with the same cations, obtained only with difficulties with the tert-butyl-containing (rac)-2 cation, afforded similar trimerized structures. The observed unusual stoichiometry and strong charge localization is tentatively assigned to the size and anisotropic charge distribution of the cations.     

Fast carbon dioxide fixation by 2,6-pyridinedicarboxamidato-nickel(II)-hydroxide complexes: influence of changes in reactive site environment on reaction rates

The planar complexes [Ni(II)(pyN(2)(R2))(OH)](-), containing a terminal hydroxo group, are readily prepared from N,N'-(2,6-C(6)H(3)R(2))-2,6-pyridinedicarboxamidate(2-) tridentate pincer ligands (R(4)N)(OH), and Ni(OTf)(2). These complexes react cleanly and completely with carbon dioxide in DMF solution in a process of CO(2) fixation with formation of the bicarbonate product complexes [Ni(II)(pyN(2)(R2))(HCO(3))](-) having η(1)-OCO(2)H ligation. Fixation reactions follow second-order kinetics (rate = k(2)'[Ni(II)-OH][CO(2)]) with negative activation entropies (-17 to -28 eu). Reactions were monitored by growth and decay of metal-to-ligand charge-transfer (MLCT) bands at 350-450 nm. The rate order R = Me > macro > Et > Pr(i) > Bu(i) > Ph at 298 K (macro = macrocylic pincer ligand) reflects increasing steric hindrance at the reactive site. The inherent highly reactive nature of these complexes follows from k(2)' ≈ 10(6) M(-1) s(-1) for the R = Me system that is attenuated by only 100-fold in the R = Ph complex. A reaction mechanism is proposed based on computation of the enthalpic reaction profile for the R = Pr(i) system by DFT methods. The R = Et, Pr(i), and Bu(i) systems display biphasic kinetics in which the initial fast process is followed by a slower first order process currently of uncertain origin.     

A Coordination Polymer of Nickel(II) Based on a Pentadentate N, S, and O Donor Ligand

The synthesis, structural characterization, and electrochemical properties of a Ni(II) complex derived from the template reaction of N,N'-bis(2-mercaptoethyl)-1,5-diazacyclooctane nickel(II), Ni-1, with ICH(2)CO(2)Na are described. Blue N-(3-thiabutyl)-N'-(3-thiapentanoate)-1,5-diazacyclooctanenickel(II)iodide, [(tbtp-daco)Ni][I], [5]I, contains Ni(II) in an octahedral environment with N(2)S(2)O(2) donor atoms; one oxygen is from an adjacent [(tbtp-daco)Ni] ion and has the same distance to Ni(II) as the intramolecular oxygen, resulting in a coordination polymer. Complex [5]I.H(2)O, C(13)H(27)N(2)O(3)S(2)NiI, crystallizes in the orthorhombic space group Pbca with a = 10.898(3), b = 18.103(5), c = 19.020(5), and Z = 8. The extent to which the polymer is retained in solution is counterion dependent, which influences redox properties (accessibility of Ni(I) and Ni(III)).     

Syntheses, properties and structures of copper and nickel complexes of 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate

The reaction of CuCl2-2H2O or NiCl2.6H2O with K2(C5H6S4) [potassium salt of 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate] under nitrogen atmosphere resulted in the isolation of [Cu(C5H6S4)2]- or [Ni(C5H6S4)2]- as the tetrabutylammonium salt. Both complexes show characteristic IR and UV-Vis absorptions of transition metal dithiolenes. Cyclic voltammograms contain two waves indicating a two step electrochemical procedure [M(C5H6S4)2]0 = [M(C5H6S4)2]1-= [M(C5H6S4)2]2-. Single crystal structure study has been carried out on the nickel complex. Crystal of [Bu4N][Ni(C5H6S4)2] belongs to monoclinic space group P21/c with a=17.576(5), 6=10.883(2), c=17.773(4) A,B=91.07(2)0, Z=4, and o(calcd.)=1.348 g/cm3. Final result is R=0.059 for 2959 reflections. The NiS4 core exhibits square planar coordination with average Ni-S bond length of 2.134(5) A. There are not anion pairs in crystal. The anions stack along a and c axes while the cations intercalate in them. The nearest S-S contact is 4.429 A. The solid powder ESR s     

Transition metal bisdithiolene complexes based on extended ligands with fused tetrathiafulvalene and thiophene moieties: new single-component molecular metals

The gold and nickel bisdithiolene complexes based on new highly extended ligands incorporating fused tetrathiafulvalene and thiophene moieties (alpha-tdt=thiophenetetrathiafulvalenedithiolate and dtdt=dihydro- thiophenetetrathiafulvalenedithiolate), were prepared and characterised by using cyclic voltammetry, single crystal X-ray diffraction, EPR, magnetic susceptibility and electrical transport measurements. These complexes, initially obtained under anaerobic conditions as diamagnetic gold monoanic [nBu(4)N][Au(alpha-tdt)(2)] (4), [nBu(4)N][Au(dtdt)(2)] (3) and nickel dianionic species [(nBu(4)N)(2)][Ni(alpha-tdt)(2)] (8), [(nBu(4)N)(2)][Ni(dtdt)(2)] (7), can be easily oxidised to the stable neutral state just by air or iodine exposure. The monoanionic complexes crystallise in at least two polymorphs, all of which have good cation and anion segregation in alternated layers, the anion layers making a dense 2D network of short SS contacts. All of the neutral complexes, obtained as microcrystalline or quasi amorphous fine powder, present relatively large magnetic susceptibilities that correspond to effective magnetic moments in the range 1-3 mu(B) indicative of high spin states and very high electrical conductivity that in case of the Ni compound can reach sigma(RT) approximately 250 S cm(-1) with a clear metallic behaviour. These compounds are new examples of the still rare single-component molecular metals.     

Activation volume measurement for C[bond]H activation. Evidence for associative benzene substitution at a platinum(II) center

The reaction of the platinum(II) methyl cation [(N-N)Pt(CH(3))(solv)](+) (N-N = ArN[double bond]C(Me)C(Me)[double bond]NAr, Ar = 2,6-(CH(3))(2)C(6)H(3), solv = H(2)O (1a) or TFE = CF(3)CH(2)OH (1b)) with benzene in TFE/H(2)O solutions cleanly affords the platinum(II) phenyl cation [(N-N)Pt(C(6)H(5))(solv)](+) (2). High-pressure kinetic studies were performed to resolve the mechanism for the entrance of benzene into the coordination sphere. The pressure dependence of the overall second-order rate constant for the reaction resulted in Delta V(++) = -(14.3 +/- 0.6) cm(3) mol(-1). Since the overall second order rate constant k = K(eq)k(2), Delta V(++) = Delta V degrees (K(eq)) + Delta V(++)(k(2)). The thermodynamic parameters for the equilibrium constant between 1a and 1b, K(eq) = [1b][H(2)O]/[1a][TFE] = 8.4 x 10(-4) at 25 degrees C, were found to be Delta H degrees = 13.6 +/- 0.5 kJ mol(-1), Delta S degrees = -10.4 +/- 1.4 J K(-1) mol(-1), and Delta V degrees = -4.8 +/- 0.7 cm(3) mol(-1). Thus DeltaV(++)(k(2)) for the activation of benzene by the TFE solvento complex equals -9.5 +/- 1.3 cm(3) mol(-1). This significantly negative activation volume, along with the negative activation entropy for the coordination of benzene, clearly supports the operation of an associative mechanism.     

Investigation of the crystal structures and magnetic features of two bis(dithiolato)nickelate salts with flexible organic cations

Transition Metal Chemistry - Two bis(dithiolato)nickel salts with different flexible ammonium counterions, [Et3MeN][Ni(dmit)2] (1) and [(i-Bu)Et3N][Ni(dmit)2] (2)...     

Kinetic evidence for intramolecular proton transfer between nickel and coordinated thiolate

The complexes [Ni(YR)(triphos)]BPh(4) (Y = S, R = Ph or Et or Y = Se, R = Ph; triphos = (Ph(2)PCH(2)CH(2))(2)PPh) have been prepared and characterized, and the X-ray crystal structure of [Ni(SPh)(triphos)]BPh(4) has been solved. In MeCN, [Ni(YR)(triphos)](+) are protonated by [lutH](+) (lut = 2,6-dimethylpyridine) to give [Ni(YHR)(triphos)](2+). Studies on the kinetics of these equilibrium reactions reveal an unexpected difference in the reactivities of [Ni(SPh)(triphos)](+) and [Ni(SEt)(triphos)](+). In both cases, the reactions exhibit a first-order dependence on the concentration of complex. When R = Ph, the dependence on the concentrations of [lutH(+)] and lut is given by k(obs) = k(1)(Ph)[lutH(+)] + k(-1)(Ph)[lut], which is typical of an equilibrium reaction where k(1)(Ph) and k(-1)(Ph) correspond to the forward and back reactions, respectively. Analogous behavior is observed for [Ni(SePh)(triphos)](+). However, for [Ni(SEt)(triphos)](+), the kinetics are more complicated, and k(obs) = (k(1)k(2)[lutH(+)] + (k(-2) + k(2)))/(k(1)[lutH(+)] + k(-1)[lut]), which is indicative of a mechanism involving two coupled equilibria in which the initial protonation of the thiolate is followed by a unimolecular equilibrium reaction that is assumed to involve the formation of an eta(2)-EtS-H ligand. The difference in reactivity between the complexes with alkyl and aryl thiolate ligands is a consequence of the (Ni(triphos))(2+) site "leveling" the basicities of these ligands. The pK(a)'s of the PhSH and EtSH constituents coordinated to the (Ni(triphos))(2+) are 16.0 and 14.6, respectively, whereas the difference in pK(a)'s of free PhSH and EtSH differ by ca. 4 units. The pK(a) of [Ni(SeHPh)(triphos)](+) is 14.4. The more strongly sigma-donating EtS ligand makes the (Ni(triphos))(2+) core sufficiently electron-rich that the basicities of the sulfur and nickel in [Ni(SEt)(triphos)](+) are very similar; therefore, the proton serves as a bridge between the two sites. The relevance of these observations to the proposed mechanisms of nickel-based hydrogenases is discussed.     

Reversible, metal-free hydrogen activation by frustrated Lewis pairs

The Lewis acid cyclohexylbis(pentafluorophenyl)boron 1, which exhibits about 15% lower Lewis acidity in comparison with B(C(6)F(5))(3), activates H(2) in the presence of the bulky Lewis bases 2,2,6,6-tetramethylpiperidine (TMP), 1,2,2,6,6-pentamethylpiperidine (PMP), tri-tert-butylphosphine (t-Bu(3)P) leading in facile reactions at room temperature to heterolytic splitting of dihydrogen and formation of the salts [TMPH][CyBH(C(6)F(5))(2)] 2, [PMPH][CyBH(C(6)F(5))(2)] 3 and [t-Bu(3)PH][CyBH(C(6)F(5))(2)] 4, which could be dehydrogenated at higher temperatures. The related Lewis acid 1-phenyl-2-[bis(pentafluorophenyl)boryl]ethane 5 exhibiting about 10% lower Lewis acidity than B(C(6)F(5))(3) is also capable of splitting H(2) in a heterolytic fashion in the presence of TMP, PMP and t-Bu(3)P yielding [TMPH][PhC(2)H(4)BH(C(6)F(5))(2)] 6, [PMPH][PhC(2)H(4)BH(C(6)F(5))(2)] 7 and [t-Bu(3)PH][PhC(2)H(4)BH(C(6)F(5))(2)] 8. Under comparable conditions as for 2-4, the dehydrogenations of 6-8 were much slower. 4b and 6 were characterized by single crystal X-ray diffraction studies.     

Mononuclear nickel(III) complexes [Ni(III)(OR)(P(C6H3-3-SiMe3-2-S)3)](-) (R = Me, Ph) containing the terminal alkoxide ligand: relevance to the nickel site of oxidized-form [NiFe] hydrogenases

The unprecedented nickel(III) thiolate [Ni (III)(OR)(P(C 6H 3-3-SiMe 3-2-S) 3)] (-) [R = Ph ( 1), Me ( 3)] containing the terminal Ni (III)-OR bond, characterized by UV-vis, electron paramagnetic resonance, cyclic voltammetry, and single-crystal X-ray diffraction, were isolated from the reaction of [Ni (III)(Cl)(P(C 6H 3-3-SiMe 3-2-S) 3)] (-) with 3 equiv of [Na][OPh] in tetrahydrofuran (THF)-CH 3CN and the reaction of complex 1 with 1 equiv of [Bu 4N][OMe] in THF-CH 3OH, respectively. Interestingly, the addition of complex 1 into the THF-CH 3OH solution of [Me 4N][OH] also yielded complex 3. In contrast to the inertness of complex [Ni (III)(Cl)(P(C 6H 3-3-SiMe 3-2-S) 3)] (-) toward 1 equiv of [Na][OPh], the addition of 1 equiv of [Na][OMe] into a THF-CH 3CN solution of [Ni (III)(Cl)(P(C 6H 3-3-SiMe 3-2-S) 3)] (-) yielded the known [Ni (III)(CH 2CN)(P(C 6H 3-3-SiMe 3-2-S) 3)] (-) ( 4). At 77 K, complexes 1 and 3 exhibit a rhombic signal with g values of 2.31, 2.09, and 2.00 and of 2.28, 2.04, and 2.00, respectively, the characteristic g values of the known trigonal-bipyramidal Ni (III) [Ni (III)(L)(P(C 6H 3-3-SiMe 3-2-S) 3)] (-) (L = SePh, SEt, Cl) complexes. Compared to complexes [Ni (III)(EPh)(P(C 6H 3-3-SiMe 3-2-S) 3)] (-) [E = S ( 2), Se] dominated by one intense absorption band at 592 and 590 nm, respectively, the electronic spectrum of complex 1 coordinated by the less electron-donating phenoxide ligand displays a red shift to 603 nm. In a comparison of the Ni (III)-OMe bond length of 1.885(2) A found in complex 3, the longer Ni (III)-OPh bond distance of 1.910(3) A found in complex 1 may be attributed to the absence of sigma and pi donation from the [OPh]-coordinated ligand to the Ni (III) center.     

(Fluoren-9-ylidene)methanedithiolato complexes of gold: synthesis, luminescence, and charge-transfer adducts

Piperidinium 9H-fluorene-9-carbodithioate and its 2,7-di-tert-butyl-substituted analogue [(pipH)(S(2)CCH(C(12)H(6)R(2)-2,7)), R = H (1a), t-Bu (1b)] and 2,7-bis(octyloxy)-9H-fluorene-9-carbodithioic acid [HS(2)CCH(C(12)H(6)(OC(8)H(17))(2)-2,7), 2] and its tautomer [2,7-bis(octyloxy)fluoren-9-ylidene]methanedithiol [(HS)(2)C=C(C(12)H(6)(OC(8)H(17))(2)-2,7), 3] were employed for the preparation of gold complexes with the (fluoren-9-ylidene)methanedithiolato ligand and its substituted analogues. The gold(I) compounds Q(2)[Au(2)(mu-kappa(2)-S,S-S(2)C=C(C(12)H(6)R(2)-2,7))(2)], where Q(+) = PPN(+) or Pr(4)N(+) for R = H (Q(2)4a) or Q(+) = Pr(4)N(+) for R = OC(8)H(17) [(Pr(4)N)(2)4c], were synthesized by reacting Q[AuCl(2)] with 1a or 2 (1:1) and excess piperidine or diethylamine. Complexes of the type [(Au(PR'3))(2)(mu-kappa(2)-S,S-S(2)C=C(C(12)H(6)R(2)-2,7))(2)] with R = H and R' = Me (5a), Et (5b), Ph (5c), and Cy (5d) or R = t-Bu and R' = Me (5e), Et (5f), Ph (5g), and Cy (5h) were obtained by reacting [AuCl(PR'(3))] with 1a,b (1:2) and piperidine. The reactions of 1a,b or 2 with Q[AuCl(4)] (2:1) and piperidine or diethylamine gave Q[Au(kappa(2)-S,S-S(2)C=C(C(12)H(6)R(2)-2,7))(2)] with Q(+) = PPN(+) for R = H [(PPN)6a], Q(+) = PPN(+) or Bu(4)N(+) for R = t-Bu (Q6b), and Q(+) = Bu(4)N(+) for R = OC(8)H(17) [(Bu(4)N)6c]. Complexes Q6a-c reacted with excess triflic acid to give [Au(kappa(2)-S,S-S(2)C=C(C(12)H(6)R(2)-2,7))(kappa(2)-S,S-S(2)CCH(C(12)H(6)R(2)-2,7))] [R = H (7a), t-Bu (7b), OC(8)H(17) (7c)]. By reaction of (Bu(4)N)6b with PhICl(2) (1:1) the complex Bu(4)N[AuCl(2)(kappa(2)-S,S-S(2)C=C(C(12)H(6)(t-Bu)(2)-2,7))] [(Bu(4)N)8b] was obtained. The dithioato complexes [Au(SC(S)CH(C(12)H(8)))(PCy(3))] (9) and [Au(n)(S(2)CCH(C(12)H(8)))(n)] (10) were obtained from the reactions of 1a with [AuCl(PCy(3))] or [AuCl(SMe(2))], respectively (1:1), in the absence of a base. Charge-transfer adducts of general composition Q[Au(kappa(2)-S,S-S(2)C=C(C(12)H(6)R(2)-2,7))(2)].1.5TCNQ.xCH(2)Cl(2) [Q(+) = PPN(+), R = H, x = 0 (11a); Q(+) = PPN(+), R = t-Bu, x = 2 (11b); Q(+) = Bu(4)N(+), R = OC(8)H(17), x = 0 (11c)] were obtained from Q6a-c and TCNQ (1:2). The crystal structures of 5c.THF, 5e.(2)/(3)CH(2)Cl(2), 5g.CH(2)Cl(2), (PPN)6a.2Me(2)CO, and 11b were solved by X-ray diffraction studies. All the gold(I) complexes here described are photoluminescent at 77 K, and their emissions can be generally ascribed to LMMCT (Q(2)4a,c, 5a-h, 10) or LMCT (9) excited states.     

A complete family of isostructural cluster compounds with cubane-like M(3)S(4)M' cores (M = Mo,W; M' = Ni,Pd, Pt): comparative crystallography and electrochemistry

By reaction of the geometrically incomplete cubane-like clusters [(eta(5)-Cp')(3)Mo(3)S(4))][pts] and [(eta(5)-Cp')(3)W(3)S(4)][pts] (Cp' = methylcyclopentadienyl; pts = p-toluenesulfonate) with group 10 alkene complexes, three new heterobimetallic clusters with cubane-like cluster cores were isolated: [(eta(5)-Cp')(3)W(3)S(4)M'(PPh(3))][pts] ([5][pts], M' = Pd; [6][pts], M' = Pt); [(eta(5)-Cp')(3)Mo(3)S(4)Ni(AsPh(3))][pts] ([7][pts]). The compounds [5][pts]-[7][pts] are completing the extensive series of clusters [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] (M = Mo, W; M' = Ni, Pd, Pt; E = P, As) which allows the consequences of replacing a single type of atom on structural and NMR and UV/vis spectroscopic as well as electrochemical properties to be determined. Single-crystal X-ray structure determinations of [5][pts]-[7][pts] revealed that [5][pts] was not isomorphous to the other members of the series [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] due to distinctly different cell parameters, which in the molecular structure of [5](+) is reflected in a slightly different orientation of the PPh(3) ligand. Electrochemical measurements on the series showed that the Mo-based clusters were more difficult to oxidize than their W-based analogues. The Pd-containing clusters underwent two-electron oxidation processes, whereas the Ni- and Pt-containing clusters underwent two separated one-electron oxidation processes.     

Gold(I) phosphido complexes: synthesis, structure, and reactivity

Deprotonation of the phosphine complexes Au(PHR(2))Cl with aqueous ammonia gave the gold(I) phosphido complexes [Au(PR(2))](n)() (PR(2) = PMes(2) (1), PCy(2) (2), P(t-Bu)(2) (3), PIs(2) (4), PPhMes (5), PHMes (6); Mes = 2,4,6-Me(3)C(6)H(2), Is = 2,4,6-(i-Pr)(3)C(6)H(2), Mes = 2,4,6-(t-Bu)(3)C(6)H(2), Cy = cyclo-C(6)H(11)). (31)P NMR spectroscopy showed that these complexes exist in solution as mixtures, presumably oligomeric rings of different sizes. X-ray crystallographic structure determinations on single oligomers of 1-4 revealed rings of varying size (n = 4, 6, 6, and 3, respectively) and conformation. Reactions of 1-3 and 5 with PPN[AuCl(2)] gave PPN[(AuCl)(2)(micro-PR(2))] (9-12, PPN = (PPh(3))(2)N(+)). Treatment of 3 with the reagents HI, I(2), ArSH, LiP(t-Bu)(2), and [PH(2)(t-Bu)(2)]BF(4) gave respectively Au(PH(t-Bu)(2))(I) (14), Au(PI(t-Bu)(2))(I) (15), Au(PH(t-Bu)(2))(SAr) (16, Ar = p-t-BuC(6)H(4)), Li[Au(P(t-Bu)(2))(2)] (17), and [Au(PH(t-Bu)(2))(2)]BF(4) (19).     

Divergent pathways of C-H bond activation: reactions of (t-Bu(3)PN)(2)TiMe(2) with trimethylaluminum

The reaction of AlMe(3) with (t-Bu(3)PN)(2)TiMe(2) 1 proceeds via competitive reactions of metathesis and C-H activation leading ultimately to two Ti complexes: [(mu(2)-t-Bu(3)PN)Ti(mu-Me)(mu(4)-C)(AlMe(2))(2)](2) 2, [(t-Bu(3)PN)Ti(mu(2)-t-Bu(3)PN)(mu(3)-CH(2))(2)(AlMe(2))(2)(AlMe(3))] 3, and the byproduct (Me(2)Al)(2)(mu-CH(3))(mu-NP(t-Bu(3))) 4. X-ray structural data for 2 and 3 are reported. Compound 3 undergoes thermolysis to generate a new species [Ti(mu(2)-t-Bu(3)PN)(2)(mu(3)-CH(2))(mu(3)-CH)(AlMe(2))(3)] 5. Monitoring of the reaction of 1 with AlMe(3) by (31)P[(1)H] NMR spectroscopy revealed intermediates including (t-Bu(3)PN)TiMe(3) 6. Compound 6 was shown to react with AlMe(3) to give 2 exclusively. Kinetic studies revealed that the sequence of reactions from 6 to 2 involves an initial C-H activation that is a second-order reaction, dependent on the concentration of Ti and Al. The second-order rate constant k(1) was 3.9(5) x 10(-4) M(-1) s(-1) (DeltaH(#) = 63(2) kJ/mol, DeltaS(#) = -80(6) J/mol x K). The rate constants for the subsequent C-H activations leading to 2 were determined to be k(2) = 1.4(2) x 10(-3) s(-1) and k(3) = 7(1) x 10(-3) s(-1). Returning to the more complex reaction of 1, the rate constant for the ligand metathesis affording 4 and 6 was k(met) = 6.1(5) x 10(-5) s(-1) (DeltaH(#) = 37(3) kJ/mol, DeltaS(#) = -203(9) J/mol x K). The concurrent reaction of 1 leading to 3 was found to proceed with a rate constant of k(obs) of 6(1) x 10(-5) s(-1) (DeltaH(#) = 62(5) kJ/mol, DeltaS(#)= -118(17) J/mol x K). Using these kinetic data for these reactions, a stochastic kinetic model was used to compute the concentration profiles of the products and several intermediates with time for reactions using between 10 and 27 equivalents of AlMe(3). These models support the view that equilibrium between 1 x AlMe(3) and 1 x (AlMe(3))(2) accounts for varying product ratios with the concentration of AlMe(3). In a similar vein, similar equilibria account for the transient concentrations of 6 and an intermediate en route to 3. The implications of these reactions and kinetic and thermodynamic data for both C-H bond activation and deactivation pathways for Ti-phosphinimide olefin polymerization catalysts are considered and discussed.