Oxidative cleavage of tetraaryltetraphosphane-1,4-diides by nickel(II) and palladium(II): formation of unusual Ni(0) and Pd(0) diaryldiphosphene complexes

[Na(2)(thf)(4)(P(4)Mes(4))] (1) (Mes = 2,4,6-Me(3)C(6)H(2)) reacts with one equivalent of [NiCl(2)(PEt(3))(2)], [NiCl(2)(PMe(2)Ph)(2)], [PdCl(2)(PBu(n)(3))(2)] or [PdCl(2)(PMe(2)Ph)(2)] to give the corresponding nickel(0) and palladium(0) dimesityldiphosphene complexes [Ni(eta(2)-P(2)Mes(2))(PEt(3))(2)] (2), [Ni(eta(2)-P(2)Mes(2))(PMe(2)Ph)(2)] (3), [Pd(eta(2)-P(2)Mes(2))(PBu(n)(3))(2)] (4) and [Pd(eta(2)-P(2)Mes(2))(PMe(2)Ph)(2)] (5), respectively, via a redox reaction. The molecular structures of the diphosphene complexes 2-5 are described.     

Synthesis and Ligand Substitution Reactions of a Mesitylphosphido-Bridged Platinum(II) Dimer

The stable primary phosphine complexes trans-M(PH(2)Mes)(2)Cl(2) (1, M = Pd; 2, M = Pt; Mes = 2,4,6-(t-Bu)(3)C(6)H(2)) were prepared from Pd(PhCN)(2)Cl(2) and K(2)PtCl(4), respectively. Reaction of Pt(COD)Cl(2) (COD = 1,5-cyclooctadiene) with less bulky arylphosphines gives the unstable cis-Pt(PH(2)Ar)(2)Cl(2) (3, Ar = Is = 2,4,6-(i-Pr)(3)C(6)H(2); 4, Ar = Mes = 2,4,6-Me(3)C(6)H(2)). Spontaneous dehydrochlorination of 4 or direct reaction of K(2)PtCl(4) with 2 equiv of PH(2)Mes gives the insoluble primary phosphido-bridged dimer [Pt(PH(2)Mes)(&mgr;-PHMes)Cl](2) (5), which was characterized spectroscopically, including solid-state (31)P NMR studies. The reversible reaction of 5 with PH(2)Mes gives [Pt(PH(2)Mes)(2)(&mgr;-PHMes)](2)[Cl](2) (6), while PEt(3) yields [Pt(PEt(3))(2)(&mgr;-PHMes)](2)[Cl](2) (7), which on recrystallization forms [Pt(PEt(3))(&mgr;-PHMes)Cl](2) (8). Complex 5 and PPh(3) afford [Pt(PPh(3))(&mgr;-PHMes)Cl](2) (9). Addition of 1,2-bis(diphenylphosphino)ethane (dppe) to 5 gives the dicationic [Pt(dppe)(&mgr;-PHMes)](2)[Cl](2) (10-Cl), which was also obtained as the tetrafluoroborate salt 10-BF(4)() by deprotonation of [Pt(dppe)(PH(2)Mes)Cl][BF(4)] (11) with Et(3)N or by reaction of [Pt(dppe)(&mgr;-OH)](2)[BF(4)](2) with 2 equiv of PH(2)Mes. Complexes 8, 9, and 10-Cl.2CH(2)Cl(2).2H(2)O were characterized crystallographically.     

Dinuclear palladium-azido complexes containing thiophene derivatives: reactivity toward organic isocyanides and isothiocyanates

Cyclopalladated tetranuclear Pd(II) complexes, [Pd2(micro-Cl)2(Y)]2 (Y = L1 or L2; H2L1 = di(2-pyridyl)-2,2'-bithiophene; H2L2 = 5,5'-di(2-pyridyl)-2,2':5',2'-terthiophene), containing two pyridyl-alpha, alpha'-disubstituted derivatives of thiophene were prepared. Treating these products with PR3 and subsequently with NaN3 produced the dinuclear Pd-azido complexes [(PR3)2(N3)Pd-Y-Pd(N3)(PR3)2] (Y = L1 or L2) or a cyclometallated complex [(PR3)(N3)Pd-Y'-Pd(N3)(PR3)] (Y' = C,N-L2). Reactions of these Pd-azido complexes with CN-Ar (Ar = 2,6-Me(2)C(6)H(3), 2,6-i-Pr(2)C(6)H(3)) or R-NCS (R = i-Pr, Et, allyl) led to the complexes containing end-on carbodiimido groups [(PMe3)2(N[double bond]C[double bond]N-Ar)Pd-Y-Pd(N[double bond]C[double bond]N-Ar)(PMe3)2] or S-coordinated tetrazole-thiolato groups {(PMe3)2[CN4(R)]S-Pd-Y-Pd-S[CN4)(R)](PMe3)2}. Interestingly, when treated with elemental sulfur, the carbodiimido complexes transformed into the cyclometallated derivatives, [(PMe3)(N[double bond]C[double bond]N-Ar)Pd-Y'-Pd(N[double bond]C[double bond]N-Ar)(PMe3)] (Y' = C,N-L1, C,N-L2). We also report the preparation of linear, thienylene-bridged dinuclear Pd complexes [L2(N3)Pd-X(or X')-Pd(N3)L2] (L = PMe3 or PMe2Ph; H2X = 2,2'-bithiophene or H2X' = 2,2':5',2'-terthiophene) and their reactivity toward organic isocyanide and isothiocyanates.     

Generation of AuPd22/Au2Pd21 analogues of the high-nuclearity Pd23(CO)20(PEt3)10 cluster containing 19-atom centered hexacapped-cuboctahedral (nu 2-octahedral) metal fragment: structural-to-synthesis approach concerning formation of Au2Pd21(CO)20(PEt3)10

Reactions of Pd(PEt(3))(2)Cl(2) and Au(PPh(3))Cl in DMF with NaOH under CO atmosphere gave rise to the unique capped three-shell homopalladium Pd(145)(CO)(x)(PEt(3))(30)(x approximately 60) and two neutral Au-Pd clusters: Au(2)Pd(21)(CO)(20)(PEt(3))(10) (1) and Au(2)Pd(41)(CO)(27)(PEt(3))(15)(following article). Similar reactions with Pd(PMe(3))(2)Cl(2) being used in place of Pd(PEt(3))(2)Cl(2) afforded Au(2)Pd(21)(CO)(20)(PMe(3))(10) (2), the trimethylphosphine analogue of, and the electronically equivalent [AuPd(22)(CO)(20)(PPh(3))(4)(PMe(3))(6)](-) monoanion (3) as the [PPh(4)](+) salt. Each of these three air-sensitive 23-atom heterometallic Au-Pd clusters was obtained in low yields (7-25%); however, their geometrical similarities with the known cuboctahedral-based homopalladium Pd(23)(CO)(20)(PEt(3))(10) (4), recently obtained in good yields from Pd(10)(CO)(12)(PEt(3))(6), suggested an alternative preparative route for obtaining. This "structure-to-synthesis" approach afforded 1 in 60-70% yields from reactions of Pd(10)(CO)(12)(PEt(3))(6) and Au(PPh(3))Cl in DMF with NaOH under N(2) atmosphere. Both the compositions and atomic arrangements for 1, 2 and 3 were unambiguously established from low-temperature single-crystal CCD X-ray crystallographic determinations in accordance with their nearly identical IR carbonyl frequencies. Cluster 1 was also characterized by (31)P[(1)H] NMR, cyclic voltammetry (CV) and elemental analysis. The virtually identical Au(2)Pd(21) core-architectures of 1 and 2 closely resemble that of 4, which consists of a centered hexa(square capped)-cuboctahedral Pd(19) fragment of pseudo-O(h) symmetry that alternatively may be viewed as a centered Pd(19)nu(2)-octahedron (where nu(n) designates (n + 1) equally spaced atoms along each edge). [AuPd(22)(CO)(20)(PPh(3))(4)(PMe(3))(6)](-) (3) in the crystalline state ([PPh(4)](+) salt) consists of two crystallographically independent monoanions 3A and 3B; a superposition analysis ascertained that their geometries are essentially equivalent. A CV indicates that reversibly undergoes two one-electron reductions and two one-electron oxidations; these reversible redox processes form the basis for an integrated structural/electronic picture that is compatible with the existence of the electronically-equivalent 1-3 along with the electronically-nonequivalent 4 (with two fewer CVEs) and other closely related species.     

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).     

Cp2Fe(PR2)2PdCl2 (R = i-Pr, t-Bu) complexes as air-stable catalysts for challenging Suzuki coupling reactions

[reaction: see text] The use of Cp(2)Fe(PR(2))(2)PdCl(2) (R = i-Pr and t-Bu) in Suzuki coupling reactions were illustrated using a high throughput screening approach. The di-tbpfPdCl(2) catalyst was shown to be the more active catalyst for unactivated and sterically challenging aryl chlorides. Comparison studies using the commercial catalysts dppfPdCl(2), (Ph(3)P)(2)PdCl(2), (Cy(3)P)(2)PdCl(2), DPEPhosPdCl(2), dppbPdCl(2), dppePdCl(2), Pd(t-Bu(3)P)(2), and [Pd(mu-Br)(t-Bu(3)P)](2) were also done for selected cases to demonstrate the superior activities of di-tbpfPdCl(2) and di-isoppfPdCl(2).     

The versatile reactivity of cyclo-(P5tBu4)- with complexes of the nickel triad

Na[cyclo-(P(5)tBu(4))] (1) reacts with [NiCl(2)(PEt(3))(2)] and [PdCl(2)(PMe(2)Ph)(2)] with elimination of tBuCl and formation of the corresponding metal(0) cyclopentaphosphene complexes [Ni{cyclo-(P(5)tBu(3))}(PEt(3))(2)] (2) and [Pd{cyclo-(P(5)tBu(3))}(PMe(2)Ph)(2)] (3). In contrast, complexes with the more labile triphenylphosphane ligand, such as [MCl(2)(PPh(3))(2)] (M=Ni, Pd), react with 1 with formation of [NiCl{cyclo-(P(5)tBu(4))}(PPh(3))] (4) and [Pd{cyclo-(P(5)tBu(4))}(2)] (5), respectively, in which the cyclo-(P(5)tBu(4)) ligand is intact. In the case of palladium, the cyclopentaphosphene complex [Pd{cyclo-(P(5)tBu(3))}(PPh(3))(2)] (6) in trace amounts is also formed. However, [Ni{cyclo-(P(5)tBu(4))}(2)] (7) is easily obtained by reaction of two equivalents of 1 and one equivalent of [NiCl(2)(bipy)] at room temperature. Complex 7 rearranges on heating in n-hexane or toluene to the previously unknown [Ni{cyclo-(P(5)tBu(4))PtBu}{cyclo-(P(4)tBu(3))}] (8), which presumably is formed via the intermediate [Ni{cyclo-(P(5)tBu(4))}{cyclo-(P(4)tBu(3))PtBu}], which, after an unexpected and unprecedented phosphanediide migration, gives 8, but always as an inseparable mixture with 7. In the reaction of 1 with [PtCl(2)(PPh(3))(2)], ring contraction and formation of [PtCl{cyclo-(P(4)tBu(3))PtBu}(PMe(2)Ph)] (9) is observed. Complexes 3-5 and 7-9 were characterised by (31)P NMR spectroscopy, and X-ray structures were obtained for 5-9.     

1,4-shifts in a dinuclear Ni(I) biarylyl complex: a mechanistic study of C-H bond activation by monovalent nickel

The known aryne complex (PEt3)2Ni(eta2-C6H2-4,5-F2) (1a) reacts with a catalytic amount of Br2Ni(PEt3)2 over 1% Na/Hg to afford the dinuclear Ni(I) biarylyl complex [(PEt3)2Ni]2(mu-eta1:eta1-3,4-F2C6H2-3',4'-F2C6H2) (2a), which results from a combination of C-C bond formation and C-H bond rearrangement. The dinuclear benzyne [(PEt3)2Ni]2(mu-eta2:eta2-C6H2-4,5-F2) (3) was obtained by the reaction of 1a with a stoichiometric amount of Br2Ni(PEt3)2 over excess 1% Na/Hg, and 3 was found to catalyze the conversion of 1a to 2a. The reaction of 1a with B(C6F5)3 produced the trinuclear complex (PEt3)3Ni3(mu3:eta1:eta1:eta2-4,5-F2C6H2)(mu3:eta1:eta1:eta2-4,5-F2C6H2-4',5'-F2C6H2) (6). The addition of PEt3 to 6 produced 1 equiv of 1a and 1 equiv of [(PEt3)2Ni]2(mu-eta1:eta1-4,5-F2C6H2-4',5'-F2C6H2) (7a). Both 6 and 7a were identified as intermediates in the conversion of 1a to 2a. The analogue [(PEt3)(PMe3)Ni]2(mu-eta1:eta1-4,5-F2C6H2-4',5'-F2C6H2) (7b) was prepared by the addition of PMe3 to 6 and was structurally characterized. NMR spectroscopic evidence identified the additional asymmetric biarylyl [(PEt3)2Ni]2(mu-eta1:eta1-4,5-F2C6H2-3',4'-F2C6H2) (8a) during the conversion of 1a to 2a. The initial observation of 2 equiv of 8a for every equivalent of 2a produced from solutions of 7a suggests that 8a and 2a are formed from a common intermediate. A crossover labeling experiment shows that the C-H bond rearrangement steps in the conversion of 1a to 2a occur with the intermolecular scrambling of hydrogen and deuterium labels. The evidence collected suggests that Ni(I) complexes are capable of activating aromatic C-H bonds.     

Sulfonate-tagged 1,4-diazabutadiene (DAD(S)) ligands and their noble-metal complexes--synthesis, characterization and immobilization in ionic liquids

A series of sulfonate-tagged 1,4-diazabutadiene (DAD(S)) ligands was prepared as salts with typical ionic liquid (IL) cations ([EMIM](+), [BMIM](+), [BMMIM](+), Bu(4)N(+), Bu(3)PMe(+), [Gua-4,4-4,4-4,1](+)). Complexation behaviour of the ligands was investigated by preparing complexes of the types [BMMIM](2)[MCl(2)(DAD(S))] (M = Pd, Pt), [BMMIM][Rh(COD)(DAD(S))] and [BMMIM](2)[Mo(CO)(4)(DAD(S))]. Using UV-Vis spectroscopy, the latter sulfonate-tagged chromophore was shown to be well soluble in the sulfonate IL [BMIM]OTf and completely insoluble in toluene, resulting in perfect immobilization. The crystal structures of [HNEt(3)](2)[2,6-Me(2)-Me-DAD(S)], [BMIM](2)[2,6-Me(2)-Me-DAD(S)], [BMMIM](2)[2,4,6-Me(3)-Me-DAD(S)], [BMMIM](2)[2,6-iPr(2)-Me-DAD(S)] and [HNEt(3)](2)[PdCl(2)(2,6-Me(2)-Me-DAD(S))] were determined. Regarding the diimine fragment, they show geometries similar to the respective non-sulfonated parent compounds.     

Copolymerization of ethylene with polar monomers: chain propagation and side reactions. A DFT theoretical study using zwitterionic Ni(II) and Pd(II) catalysts

Calculations utilizing anionic substituted derivates of the cationic N(wedge)N--Ni(II) and Pd(II) diimine Brookhart complex have been carried out on the barriers of ethylene and acrylonitrile insertion into a M- methyl, propyl and CH(CN)Et bond for M = Ni, Pd. The possibility of side reactions such as chelate formation with the polar functionality and oligomerization of the active species after acrylonitrile insertion are explored. The diimine ring system N--N = -NR' 'CR(1)CR(2)NR' ' with R' ' = 2,6-C(6)H(3)(i-Pr)(2) and R(1),R(2) = Me was functionalized by adding one or two anionic groups (BF(3)(-), etc.) in place of i-Pr on the aryl rings or by replacing one Me diimine backbone group (R(1)) with BH(3)(-). The objective of this investigation is computationally to design catalysts for ethylene/acrylonitrile copolymerization that have activities that are comparable to that of the cationic Ni(II) diimine or at least the Pd(II) diimine Brookhart system for ethylene homopolymerization. Complexes that might meet this objective are discussed.     

Effects of vacuum on tetrakis-isocyanide complexes of silver(I) and copper(I): Implications for sims analyses

Vacuum-promoted ligand loss has been detected for the complexes [Ag(CNMe)(4)]PF(6) (Me = methyl), [Ag(CN-t-Bu)(4)]ClO(4) (t-Bu = tert-butyl) and [Ag(CNCy)(4)]ClO(4) (Cy = cyclohexyl). The analogous Cu(I) isocyanide complexes are stable under the same conditions. These conclusions are based on infrared spectroscopy, secondary-ion mass-spectrometry (SIMS) and weight-loss measurements.     

Synthesis, structural characterization, reactivity, and thermal stability of [eta(5):sigma-Me2C(C5H4)(C2B10H10)]Ti(R)(NMe2)

Reaction of [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]TiCl(NMe2) (1) with 1 equiv of PhCH2K, MeMgBr, or Me3SiCH2Li gave corresponding organotitanium alkyl complexes [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(R)(NMe2) (R = CH2Ph (2), CH2SiMe3 (4), or Me (5)) in good yields. Treatment of 1 with 1 equiv of n-BuLi afforded the decomposition product {[eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti}2(mu-NMe)(mu:sigma-CH2NMe) (3). Complex 5 slowly decomposed to generate a mixed-valence dinuclear species {[eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti}2(mu-NMe2)(mu:sigma-CH2NMe) (6). Complex 1 reacted with 1 equiv of PhNCO or 2,6-Me2C6H3NC to afford the corresponding monoinsertion product [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(Cl)[eta(2)-OC(NMe2)NPh] (7) or [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(Cl)[eta(2)-C(NMe2)=N(2,6-Me2C6H3)] (8). Reaction of 4 or 5 with 1 equiv of R'NC gave the titanium eta(2)-iminoacyl complexes [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(NMe2)[eta(2)-C(R)=N(R')] (R = CH2SiMe3, R' = 2,6-Me2C6H3 (9) or tBu (10); R = Me, R' = 2,6-Me2C6H3 (11) or tBu (12)). The results indicated that the unsaturated molecules inserted into the Ti-N bond only in the absence of the Ti-C(alkyl) bond and that the Ti-C(cage) bond remained intact. All complexes were fully characterized by various spectroscopic techniques and elemental analyses. Molecular structures of 2, 3, 6-8, and 10-12 were further confirmed by single-crystal X-ray analyses.     

Synthesis and crystal structure of unprecedented phosphine adducts of d(1)-aryl imido-vanadium(IV) complexes

The reaction of the imido precursor [V(NAr)Cl(2)](n)() (1) (Ar = 2,6-i-Pr(2)C(6)H(3)) with 3 equiv of PMe(2)Ph yields the monomeric complex [V(=NAr)Cl(2)(PMe(2)Ph)(2)] (2). Reacting 1 with 1.5 equiv of dmpe or 1 equiv of dppm affords the dimeric complexes [V(=NAr)Cl(2)(dmpe)](2)(mu-P,P'-dmpe) (3) and [V(=NAr)Cl(2)(dppm)](2) (4), respectively. Complexes 2-4 have been fully characterized by spectroscopic methods, magnetism studies, and X-ray crystallography.     

烷氧基钨配合物的合成及β-H消去反应

氢基钨配合物;烷氧基钨配合物的合成及β-H消去反应     

Mechanistic insight into protonolysis and cis-trans isomerization of benzylplatinum(II) complexes assisted by weak ligand-to-metal interactions. A combined kinetic and DFT study

Low-temperature NMR measurements showed that protonolysis and deuterolysis by H(D)X acids on meta- and para-substituted dibenzylplatinum(II) complexes cis-[Pt(CH(2)Ar)(2)(PEt(3))(2)] (Ar = C(6)H(4)Y(-); Y = 4-Me, 1a; 3-Me, 1b; H, 1c; 4-F, 1d; 3-F, 1e; 4-Cl, 1f; 3-Cl, 1g; 3-CF(3), 1h) in CD(3)OD leads directly to the formation of trans-[Pt(CH(2)Ar)(PEt(3))(2)(CD(3)OD)]X (4a-4h) and toluene derivatives. The reaction obeys the rate law k(obsd) = k(H)[H(+)]. For CH(2)Ar = CH(2)C(6)H(5)(-), k(H) = 176 ± 3 M(-1) s(-1) and k(D) = 185 ± 5 M(-1) s(-1) at 298.2 K, ΔH(double dagger) = 46 ± 1 kJ mol(-1) and ΔS(double dagger) = -47 ± 1 J K(-1) mol(-1). In contrast, in acetonitrile-d(3), three subsequent stages can be distinguished, at different temperature ranges: (i) instantaneous formation of new benzylhydridoplatinum(IV) complexes cis-[Pt(CH(2)Ar)(2)(H)(CD(3)CN)(PEt(3))(2)]X (2a-2h, at 230 K), (ii) reductive elimination of 2a-2h to yield cis-[Pt(CH(2)Ar)(CD(3)CN)(PEt(3))(2)]X (3a-3h) and toluene derivatives (in the range 230-255 K), and finally (iii) spontaneous isomerization of the cis cationic solvento species to the corresponding trans isomers (4a-4h, in the range 260-280 K). All compounds were detected and fully characterized through their (1)H and (31)P{(1)H} NMR spectra. Kinetics monitored by (1)H and (31)P{(1)H} NMR and isotopic scrambling experiments on cis-[Pt(CH(2)Ar)(2)(H)(CD(3)CN)(PEt(3))(2)]X gave some insight onto the mechanism of reductive elimination of 2a-2h. Systematic kinetics of isomerization of 3a-3h were followed in the temperature range 285-320 K by stopped-flow techniques. The process goes, as expected, through the relatively slow dissociative loss of the weakly bonded solvent molecule and interconversion of two geometrically distinct T-shaped three-coordinate intermediates. The dissociation energy depends upon the solvent-coordinating ability. DFT optimization reveals that along the energy profile the "cis-like" [Pt(CH(2)Ar)(PMe(3))(2)](+) intermediate is strongly stabilized by a Pt···η(2)-C1-C(ipso) bond between the unsaturated metal and benzyl carbons. The value of the ensuing stabilization energy was estimated by computational data to be greater than that found for similar β-agostic Pt···η(2)-CH interactions with alkyl groups containing β-hydrogens. An observed consequence of the strong stabilization of "cis"-[Pt(η(2)-CH(2)Ar)(PMe(3))(2)](+) is the remarkable acceleration of the rate of isomerization, greater than that produced by the so-called "β-hydrogen kinetic effect". Kinetic and DFT data concur to indicate that electron donation by substituents on the benzyl ring leads to further stabilization of the "cis"-[Pt(η(2)-CH(2)Ar)(PMe(3))(2)](+) cationic species.     

Aryl-fluoride reductive elimination from Pd(II): feasibility assessment from theory and experiment

DFT methods were used to elucidate features of coordination environment of Pd(II) that could enable Ar-F reductive elimination as an elementary C-F bond-forming reaction potentially amenable to integration into catalytic cycles for synthesis of organofluorine compounds with benign stoichiometric sources of F(-). Three-coordinate T-shaped geometry of Pd(II)Ar(F)L (L = NHC, PR(3)) was shown to offer kinetics and thermodynamics of Ar-F elimination largely compatible with synthetic applications, whereas coordination of strong fourth ligands to Pd or association of hydrogen bond donors with F each caused pronounced stabilization of Pd(II) reactant and increased activation barrier beyond the practical range. Decreasing donor ability of L promotes elimination kinetics via increasing driving force and para-substituents on Ar exert a sizable SNAr-type TS effect. Synthesis and characterization of the novel [Pd(C(6)H(4)-4-NO(2))ArL(mu-F)](2) (L = P(o-Tolyl)(3), 17; P(t-Bu)(3), 18) revealed stability of the fluoride-bridged dimer forms of the requisite Pd(II)Ar(F)L as the key remaining obstacle to Ar-F reductive elimination in practice. Interligand steric repulsion with P(t-Bu)(3) served to destabilize dimer 18 by 20 kcal/mol, estimated with DFT relative to PMe(3) analog, yet was insufficient to enable formation of greater than trace quantities of Ar-F; C-H activation of P(t-Bu)(3) followed by isobutylene elimination was the major degradation pathway of 18 while Ar/F- scrambling and Ar-Ar reductive elimination dominated thermal decomposition of 17. However, use of Buchwald's L = P(C(6)H(4)-2-Trip)(t-Bu)(2) provided the additional steric pressure on the [PdArL(mu-F)](2) core needed to enable formation of aryl-fluoride net reductive elimination product in quantifiable yields (10%) in reactions with both 17 and 18 at 60 degrees over 22 h.     

A mechanistic investigation of the polymerization of ethylene catalyzed by neutral Ni(II) complexes derived from bulky anilinotropone ligands

An extensive mechanistic investigation has been carried out on ethylene polymerizations catalyzed by neutral Ni(II) catalysts derived from bulky anilinotropone ligands. Complexes and precatalysts prepared include aryl derivatives [(2,6-i-Pr(2)C(6)H(3))NC(7)H(4)O(7-Aryl)Ni(Ph)(PPh(3))] (9, Aryl = phenyl(a), 1-naphthyl(b), p-methoxyphenyl(c), p-trifluoromethylphenyl(d)), alkyl derivatives [[(2,6-(i)Pr(2)C(6)H(3))NC(7)H(5)O]Ni(R)(2,4-lutidine)] (16, R = Et (a), n-Pr (b)) and [[(2,6-(i)Pr(2)C(6)H(3))NC(7)H(5)O]Ni(R)(PPh(3))] (17, R = Et (a), n-Pr (b), n-hexyl (c), i-Pr (d)), and the nickel hydride complex [[(2,6-(i)Pr(2)C(6)H(3))NC(7)H(5)O]Ni(H)(PPh(3))], 20. Branched polyethylenes are produced at 40-80 degrees C in toluene with M(n) values in the 100-200K range and molecular weight distributions of ca. 1.4-2.2. Branching ranges from 15 to 64 branches/1000 carbons depending on temperature and ethylene pressure. The electron-withdrawing -CF(3) substituent on the 7-aryl group increases activity but has little effect on branching and molecular weight. NMR experiments establish that in the case of the PPh(3)-substituted systems, the catalyst rests as an equilibrating mixture of the alkyl phosphine and the alkyl ethylene complexes. At high ethylene pressures, the turnover frequency saturates, indicating that the equilibrium has shifted nearly completely to the alkyl olefin complex. Under these conditions, the barriers to migratory insertion were determined to be ca. 16-17 kcal/mol for 9a, 9c, 9d, and 16a. Extraction of 2,6-lutidine from complexes 16a,b yields highly dynamic beta-agostic alkyl complexes [[(2,6-i-Pr(2)C(6)H(3))NC(7)H(5)O]Ni(Et)] 21 and [[(2,6-i-Pr(2)C(6)H(3))NC(7)H(5)O]Ni(i-Pr)] 22. Free energy barriers to nickel-carbon bond rotation and beta-hydride elimination of 11.1 and ca. 17 kcal/mol, respectively, were determined for 22. Themolysis of 17c at 50 degrees C generates hydride 20 and hexene and occurs by two pathways, one independent of [PPh(3)] and one retarded by PPh(3). At much slower rates, hydride 20 reductively eliminates free ligand, which ultimately generates a bis-ligand complex, 25. Catalyst decay under polymerization conditions was shown to occur by a similar process to generate free ligand and a bis-ligand complex formed by reaction of free ligand with an active catalyst species. The major chain transfer route is a simple beta-elimination process, not chain transfer to monomer.     

Tri-chlorido, 2-methylallyl and 2-butenyl tert-butylimido niobium and tantalum complexes: synthesis, multinuclear NMR spectroscopy and reactivity

Pseudooctahedral complexes [MCl(3)(NtBu)L(2)] (M = Nb, L = py 1, ? tmeda 3; M = Ta, L = py 2, ? tmeda 4) have been studied by spectroscopic methods. By a VT (1)H NMR experiment a mutual exchange process between the py(ax) and py(free) in the complexes 1-2 was observed, whereas (13)C and (15)N NMR studies showed in the complexes 3-4 a tmeda ligand with an axial/equatorial coordination mode. The reaction of 2 with 3 equiv of Grignard reagent produces the methathesis products [TaR(3)(NtBu)] (R = CH(2)CMeCH(2)5, CH(2)CHCHCH(3)6) in which 2-methylallyl and 2-butenyl groups appear with a η(3)- and σ-coordination mode, respectively. When, toluene solutions of the compounds 5-6 were treated with 2 equiv of 2,6-dimethylphenylisocyanide the imido bisiminoacyl compounds [TaR(NtBu){C(R)NAr-κ(1)C}(2)] (Ar = 2,6-Me(2)C(6)H(3); R = CH(2)CMeCH(2)7, CH(2)CHCHCH(3)8) can be isolated, via an imido iminoacyl intermediate [TaR(2)(NtBu){C(R)NAr-κ(1)C}] (Ar = 2,6-Me(2)C(6)H(3); R = CH(2)CMeCH(2)9) as we have observed in the treatment of 5 with 1 equiv of isocyanide; however, the analogous reaction between 5 and COPh(2) leads to the formation of the trisalkoxo imido compound [Ta(OCPh(2)R)(3)(NtBu)] (R = CH(2)CMeCH(2)10). All new complexes were studied by IR and multinuclear NMR spectroscopy.     

Differing reactivities of (trimpsi)M(CO)(2)(NO) complexes [M = V,Nb, Ta; trimpsi = (t)BuSi(CH(2)PMe(2))(3)] with halogens and halogen sources

Treatment of (trimpsi)V(CO)(2)(NO) (trimpsi = (t)BuSi(CH(2)PMe(2))(3)) with 1 equiv of PhICl(2) or C(2)Cl(6) or 2 equiv of AgCl affords (trimpsi)V(NO)Cl(2) (1) in moderate yields. Likewise, (trimpsi)V(NO)Br(2) (2) and (trimpsi)V(NO)I(2) (3) are formed by the reactions of (trimpsi)V(CO)(2)(NO) with Br(2) and I(2), respectively. The complexes (trimpsi)M(NO)I(2)(PMe(3)) (M = Nb, 4; Ta, 5) can be isolated in moderate to low yields when the (trimpsi)M(CO)(2)(NO) compounds are sequentially treated with 1 equiv of I(2) and excess PMe(3). The reaction of (trimpsi)V(CO)(2)(NO) with 2 equiv of ClNO forms 1 in low yield, but the reactions of (trimpsi)M(CO)(2)(NO) (M = Nb, Ta) with 1 equiv of ClNO generate (trimpsi)M(NO)(2)Cl (M = Nb, 6; Ta, 7). Complexes 6 and 7 are thermally unstable and decompose quickly at room temperature; consequently, they have been characterized solely by IR and (31)P[(1)H] NMR spectroscopies. All other new complexes have been fully characterized by standard methods, and the solid-state molecular structures of 1.3CH(2)Cl(2), 4.(3/4)CH(2)Cl(2), and 5.THF have been established by single-crystal X-ray diffraction analyses. A convenient method of generating Cl(15)NO has also been developed during the course of these investigations.     

Preparation, characterization, and magnetic behavior of the ln derivatives (ln = nd, la) of a 2,6-diiminepyridine ligand and corresponding dianion

An unprecedented Nd[2,6-[[2,6-(i-Pr)(2)C(6)H(5)]N=C(CH(3))](2)(C(5)H(3)N)]NdI(2)(THF) (1) complex was prepared by oxidizing metallic Nd with I(2) in THF and in the presence of 2,6-[[2,6-(i-Pr)(2)C(6)H(5)]N=C(CH(3))](2)(C(5)H(3)N). The magnetic behavior at variable T clearly indicated that the complex should be regarded as a trivalent Nd atom antiferromagnetically coupled to a radical anion. By using the doubly deprotonated form of the diimino pyridine ligand [[2,6-[[2,6-(i-Pr)(2)C(6)H(5)]N-C=CH(2)](2)(C(5)H(3)N)](2-) (2) the corresponding trivalent complexes [[2,6-[[2,6-(i-Pr)(2)C(6)H(5)]N-C=CH(2)](2)(C(5)H(3)N)]Ln (THF)](mu-Cl)(2)[Li(THF)(2)].0.5 (hexane) [Ln = Nd (3), La (4)] were obtained and characterized. Reduction of these species afforded electron transfer to the ligand system which gave ligand dimerization via C-C bond formation through one of the two ene-amido functions of each molecule. The resulting dinuclear [[([2,6-(i-Pr)(2)C(6)H(5)]N-C=(CH(2)))(C(5)H(3)N)([2,6-(i-Pr)(2)C(6)H(5)]N=CCH(2))]Ln(THF)(2)(mu-Cl)[Li(THF)(3)])(2).2(THF) [Ln = Nd (5), La (6)] were isolated and characterized.