Rhenium complexes of tris(pyrazolyl)methanes and sulfonate derivative

The trioxo [ReO(3){SO(3)C(pz)(3)}] (1) (pz = pyrazolyl) and oxo [ReOCl{SO(3)C(pz)(3)}(PPh(3))]Cl (2) compounds with tris(pyrazolyl)methanesulfonate were obtained by treatment of Re(2)O(7) or [ReOCl(3)(PPh(3))(2)], respectively, with Li[SO(3)C(pz)(3)], whereas [ReCl(3){HC(pz)(3)}] (3), [ReCl(3){HC(3,5-Me(2)pz)(3)}] (4) and [ReCl(4){eta(2)-HC(pz)(3)}] (5) were prepared by reaction of [ReOCl(3)(PPh(3))(2)] (3,4) or [ReCl(4)(NCMe)(2)] (5) with hydrotris(pyrazolyl)methane HC(pz)(3) (3,5) or hydrotris(3,5-dimethyl-1-pyrazolyl)methane HC(3,5-Me(2)pz)(3) (4). [ReO{SO(3)C(pz)(3)}{OC(CH(3))(2)pz}][ReO(4)] 6, with a chelated pyrazolyl-alkoxide, was derived from an unprecedented ketone-pyrazolyl coupling on reaction of crude 1 with acetone. The compounds have been characterized by elemental analyses, IR and NMR spectroscopies, FAB-MS spectrometry and cyclic voltammetry and, in the case of 5 and 6, also by single-crystal X-ray diffraction. The electrochemical E(L) Lever parameter has been estimated, for the first time, for the SO(3)C(pz)(3)(-) and oxo ligands allowing the measurement of their electron-donor character and comparison with other ligands. Compounds 1, 2 and 6 appear to be the first tris(pyrazolyl)methanesulfonate complexes of rhenium to be reported.     

Proton-induced reactivities of ruthenium azido complexes: the first example of boron-carbon bond formation by methylene insertion into a B-H bond

Whereas the reaction of Tp(PhCN)(PPh(3))Ru-N(3) {Tp = HB(pz)(3), pz = pyrazolyl} with CH(3)I in CH(2)Cl(2) led to the cationic ruthenium methyleneimine complex [Tp(PPh(3))(PhCN)Ru(NH=CH(2))]I, the analogous reaction with HCl gave rise to the ruthenium chloride complex containing a methyl tris(pyrazolyl)borate ligand (Me)Tp(PPh(3))(PhCN)RuCl, as a result of the highly unusual methylene insertion into a B-H bond of the Tp ligand.     

Isomerism in rhodium(I) N,S-donor heteroscorpionates: ring substituent and ancillary ligand effects

The heteroscorpionate ligands [HB(taz)(2)(pz(R))](-) (pz(R) = pz, pz(Me2), pz(Ph)) and [HB(taz)(pz)(2)](-), synthesised from the appropriate potassium hydrotris(pyrazolyl)borate salt and 4-ethyl-3-methyl-5-thioxo-1,2,4-triazole (Htaz), react with [{Rh(cod)(μ-Cl)}(2)] to give [Rh(cod)Tx] {Tx = HB(taz)(2)(pz), HB(taz)(2)(pz(Me2)), HB(taz)(2)(pz(Ph)), HB(taz)(pz)(2)}; the heteroscorpionate rhodaboratrane [Rh{B(taz)(2)(pz(Me2))}{HB(taz)(2)(pz(Me2))}] is the only isolable product from the reaction of [{Rh(nbd)(μ-Cl)}(2)] with K[HB(taz)(2)(pz(Me2))]. Carbonylation of the cod complexes gave a mixture of [Rh(CO)(2)Tx] and [(RhTx)(2)(μ-CO)(3)] which reacts with PR(3) to give [Rh(CO)(PR(3))Tx] (R = Cy, NMe(2), Ph, OPh). In the solid state the complexes are square planar with the particular structure dependent on the steric and/or electronic properties of the scorpionate and ancillary ligands. The complex [Rh(cod){HB(taz)(pz)(2)}] has the heteroscorpionate κ(2)[N(2)]-coordinated to rhodium with the B-H bond directed away from the rhodium square plane while [Rh(cod){HB(taz)(2)(pz(Me2))}] is κ(2)[SN]-coordinated, with the B-H bond directed towards the metal. The complexes [Rh(CO)(PPh(3)){HB(taz)(2)(pz)}] and [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Me2))}] are also κ(2)[SN]-coordinated but with the pyrazolyl ring cis to PPh(3); in the former the B-H bond is directed towards rhodium while in the latter the ring is pseudo-parallel to the rhodium square plane, as also found for [Rh(CO)(2){HB(taz)(2)(pz(Me2))}]. The analogues [Rh(CO)(PR(3)){HB(taz)(2)(pz(Me2))}] (R = Cy, NMe(2)) have the phosphines trans to the pyrazolyl ring. Uniquely, [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Ph))}] is κ(2)[S(2)]-coordinated. A qualitative mechanism is given for the rapid ring-exchange, and hence isomerisation, observed in solution.     

Unusual reactivity of tris(pyrazolyl)borate zirconium benzyl complexes

The synthesis and reactivity of [Tp*Zr(CH2Ph)2][B(C6F5)4] (2, Tp* = HB(3,5-Me2pz)3, pz = pyrazolyl) have been explored to probe the possible role of Tp'MR2+ species in group 4 metal Tp'MCl3/MAO olefin polymerization catalysts (Tp' = generic tris(pyrazolyl)borate). The reaction of Tp*Zr(CH2Ph)3 (1) with [Ph3C][B(C6F5)4] in CD2Cl2 at -60 degrees C yields 2. 2 rearranges rapidly to [{(PhCH2)(H)B(mu-Me2pz)2}Zr(eta2-Me2pz)(CH2Ph)][B(C6F5)4] (3) at 0 degrees C. Both 2 and 3 are highly active for ethylene polymerization and alkyne insertion. Reaction of 2 with excess 2-butyne yields the double insertion product [Tp*Zr(CH2Ph)(CMe=CMeCMe=CMeCH2Ph)][B(C6F5)4] (4). Reaction of 3 with excess 2-butyne yields [{(PhCH2)(H)B(mu-Me2pz)2}Zr(Cp*)(eta2-Me2pz)][B(C6F5)4] (6, Cp* = C5Me5) via three successive 2-butyne insertions, intramolecular insertion, chain walking, and beta-Cp* elimination.     

A novel transformation of a zirconium imido compound and the development of a new class of N3 donor heteroscorpionate ligand

Reaction of the dimeric zirconium imido compound [Zr2(mu-NAr)2Cl4(THF)4] with tris(3,5-dimethylpyrazolyl)methyl silane very selectively gave [Zr{(Me2pz)2Si(Me)NAr}Cl3] (1), a highly active pre-catalyst for ethylene polymerisation; a more general and versatile route to N3 donor heteroscorpionate compounds was achieved via the protio ligand (Me2pz)2CHSi(Me)2N(H)iPr for which neutral and cationic organometallic Group 3 and 4 derivatives are reported (Ar = 2,6-C6H(3)iPr2).     

Synthesis, structures, and DFT bonding analysis of new titanium hydrazido(2-) complexes

The reaction of 1,1-diphenylhydrazine with Ti(NMe2)2Cl2 produced the monomeric terminal titanium hydrazido(2-) species Ti(NNPh2)Cl2(HNMe2)2 (1) in near-quantitative yield. The reaction of Ti(NMe2)2Cl2 with the less sterically demanding ligand precursors 1,1-dimethylhydrazine or N-aminopiperidine gave the dimeric mu-eta2,eta1-bridged compounds Ti2(mu-eta2,eta1-NNMe2)2Cl4(HNMe2)2 (2) and Ti2[mu-eta2,eta1-NN(CH2)5]2Cl4(HNMe2)3 (3). The X-ray structures of 2 and 3 showed the formation of N-H...Cl hydrogen bonded dimers or chains, respectively. The reaction of 1 with an excess of pyridine formed [Ti(NNPh2)Cl2(py)2]n (4, n = 1 or 2). The reaction of the tert-butyl imido complex Ti(N(t)Bu)Cl2(py)3 with either 1,1-dimethylhydrazine or N-aminopiperidine again resulted in the formation of hydrazido-bridged dimeric complexes, namely Ti2(mu-eta2,eta1-NNMe2)2Cl4(py)2 (5, structurally characterized) and Ti2[mu-eta2,eta1-NN(CH2)5]2Cl4(py)2 (6). Compounds 1 and 4 are potential new entry points into terminal hydrazido(2-) chemistry of titanium. Compound 1 reacted with neutral fac-N3 donor ligands to form Ti(NNPh2)Cl2(Me3[9]aneN3) (7), Ti(NNPh2)Cl2(Me3[6]aneN3) (8), Ti(NNPh2)Cl2[HC(Me2pz)3] (9, structurally characterized), and Ti(NNPh2)Cl2[HC(n)Bupz)3] (10) in good yields (Me3[9]aneN3 = trimethyl-1,4,7-triazacyclononane, Me3[6]aneN3 = trimethyl-1,3,5-triazacyclohexane, HC(Me2pz)3 = tris(3,5-dimethylpyrazolyl)methane, and HC((n)Bupz)3 = tris(4-(n)butylpyrazolyl)methane). DFT calculations were performed on both the model terminal hydrazido compound Ti(NNPh2)Cl2[HC(pz)3] (I) and the corresponding imido compounds Ti(NMe)Cl2[HC(pz)3] (II) and Ti(NPh)Cl2[HC(pz)3] (III). The NNPh2 ligand binds to the metal center in an analogous manner to that of terminal imido ligands (metalligand triple bond), but with one of the Ti=N(alpha) pi components significantly destabilized by a pi interaction with the lone pair of the N(beta) atom. The NR ligand sigma donor ability was found to be NMe > NPh > NNPh2, whereas the overall (sigma + pi) donor ability is NMe > NNPh2 > NPh, as judged by fragment orbital populations, Ti-N atom-atom overlap populations, and fragment-charge analysis. DFT calculations on the hydrazido ligand in a mu-eta2,eta1-bridging mode showed involvement of the N=N pi electrons in donation to one of the Ti centers. This TiN2 interaction is best represented as a metallocycle.     

Rhenium and technetium tricarbonyl complexes anchored by pyrazole-based tripods: novel lead structures for the design of myocardial imaging agents

This report describes the synthesis and biological evaluation of cationic (99m)Tc-tricarbonyl complexes anchored by ether-containing tris(pyrazolyl)methane or bis(pyrazolyl)ethanamine ligands to be applied in the design of radiopharmaceuticals for myocardial imaging: fac-[(99m)Tc(CO)(3){RC(pz)(3)}](+) (R = H (1a), MeOCH(2) (2a), EtOCH(2) (3a), (n)PrOCH(2) (4a)) and fac-[(99m)Tc(CO)(3){RNHCH(2)CH(pz)(2)}](+) (R = H (5a), MeO(CH(2))(2) (6a)) (pz = pyrazolyl). At the no carrier added level, complexes 1a-6a were obtained in high radiochemical yield (> 98%) by reaction of fac-[(99m)Tc(CO)(3)(H(2)O)(3)](+) with the corresponding tripod chelator in aqueous medium. All these complexes display a high in vitro and in vivo stability, except 6a which metabolizes in vivo yielding fac-[(99m)Tc(CO)(3){HO(CH(2))(2)NHCH(2)CH(pz)(2)}](+) (7a). Biological studies in mice have shown that among the radiotracers evaluated in this work, 3a, anchored by a tris(pyrazolyl)methane chelator bearing an ethyl methyl ether substituent, has the highest heart uptake (3.6 +/- 0.5%ID g(-1) at 60 min p.i.). Complex 3a presents also the best heart: blood, heart: liver and heart: lung ratios, appearing as the most promising as a potential myocardial imaging agent. The chemical identity of 1a-7a was ascertained by HPLC comparison with the previously reported fac-[Re(CO)(3){HC(pz)(3)}]Br (1) and with the novel fac-[Re(CO)(3){RC(pz)(3)}]Br (R = MeOCH(2) (2), EtOCH(2) (3), (n)PrOCH(2)(4)) and fac-[Re(CO)(3){RNHCH(2)CH(pz)(2)}]Br (R = H (5), MeO(CH(2))(2) (6) HO(CH(2))(2) (7)). The novel Re(I) tricarbonyl complexes, 2-7, were characterized by the common analytical techniques, including single crystal X-ray diffraction analysis. The solid state structure confirmed the presence of facial and tridentate (kappa(3)-N(3)) anchor ligands. Solution NMR studies have also shown that this kappa(3)-N(3) coordination mode is retained in solution for all complexes (2-7).     

Imidotitanium Tris(pyrazolyl)hydroborates: Synthesis, Solution Dynamics, and Solid-State Structure

Reaction of [Ti(NBu(t))Cl(2)(py-Bu(t))(2)] (1; py-Bu(t) = 4-tert-butyl pyridine) with 1 equivalent of K[Tp(Me2)], K[Tp(Pri)] or K[Tp(Pri,Br)] affords the corresponding complexes [Tp(Me2)Ti(NBu(t))Cl(py-Bu(t))] (2), [Tp(Pri)Ti(NBu(t))Cl(py-Bu(t))] (3), and [Tp(Pri,Br)Ti(NBu(t))Cl(py-Bu(t))] (4), respectively, which are the first examples of imido Group 4 tris(pyrazolyl)hydroborates [Tp(Me2) = tris(3,5-dimethylpyrazolyl)hydroborate; Tp(Pri) = tris(3-isopropylpyrazolyl)hydroborate; Tp(Pri,Br) = tris(3-isopropyl-4-bromopyrazolyl)hydroborate]. Complexes 2-4 are fluxional on the (1)H and (13)C NMR time scales, the spectra indicating restricted rotation about the Ti-py-Bu(t) bond. Activation parameters for this dynamic process have been determined both by (13)C NMR lineshape analysis and by coalescence measurements. The solution-state structure for 2 has been unambiguously assigned from a low temperature, phase-sensitive (1)H NOESY DQF spectrum and the solid-state X-ray crystal structure of the dichloromethane solvate of 3 has been determined (space group P2(1)/n; a = 12.539(3), b = 14.686(3), c = 21.747(4) ?; beta = 91.28(3) degrees; R(1) = 0.0694 and wR(2) = 0.154 for 1578 observed reflections). (13)C NMR Deltadelta values (Deltadelta = delta(C(alpha)) - delta(C(beta))) for the tert-butyl imido ligand in 2-4 suggest that the donor ability of the tris(pyrazolyl)hydroborate ligands increases in the order Tp(Pri,Br) < Tp(Pri) < Tp(Me2). None of these ligands, however, is as effective a donor to the metal center as either eta-C(5)H(5) or eta-C(5)Me(5).     

Structural comparisons of silver(I) complexes of third-generation ligands built from tridentate (o-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2)) versus bidentate poly(1-pyrazolyl)methane units (o-C(6)H(4)[CH(2)OCH(2)CH(pz)(2)](2)) (pz = pyrazolyl ring)

The new bitopic, bis(1-pyrazolyl)methane-based ligand o-C6H4[CH2OCH2CH(pz)2]2 (L2, pz = pyrazolyl ring) is prepared from the reaction of (pz)2CHCH2OH (obtained from the reduction of (pz)2CHCOOH with BH3.S(CH3)2) with NaH, followed by the addition of alpha,alpha'-dibromo-o-xylene. The reaction of L2 with AgPF6 or AgO3SCF3 yields {o-C6H4[CH2OCH2CH(pz)2]2(AgPF6)}n or {o-C6H4[CH2OCH2CH(pz)2]2(AgO3SCF3)}n, respectively. Both compounds in the solid state have tetrahedral silver(I) centers arranged in a 1D coordination polymer network. The analogous ligand based on tris(1-pyrazolyl)methane units, o-C6H4[CH2OCH2C(pz)3]2 (L3), reacts with AgO3SCF3 to form a similar coordination polymer, {o-C6H4[CH2OCH2C(pz)3]2(AgO3SCF3)}n. In this case, each tris(pyrazolyl)methane unit in L3 adopts the kappa2-kappa0 bonding mode. Crystallization of a 3:1 mixture of AgO3SCF3 and L3 yields {o-C6H4[CH2OCH2C(pz)3]2(AgO3SCF3)2}n, in which the tris(1-pyrazolyl)methane units adopt a kappa2-kappa1 coordination mode.     

Syntheses of Cationic, Six-Coordinate Cadmium(II) Complexes Containing Tris(pyrazolyl)methane Ligands. Influence of Charge on Cadmium-113 NMR Chemical Shifts

Treating a thf (thf = tetrahydrofuran) suspension of Cd(acac)(2) (acac = acetylacetonate) with 2 equiv of HBF(4).Et(2)O results in the immediate formation of [Cd(2)(thf)(5)](BF(4))(4) (1). Crystallization of this complex from thf/CH(2)Cl(2) yields [Cd(thf)(4)](BF(4))(2) (2), a complex characterized in the solid state by X-ray crystallography. Crystal data: monoclinic, P2(1)/n, a = 7.784(2) ?, b = 10.408(2) ?, c = 14.632(7) ?, beta = 94.64(3) degrees, V = 1181.5(6) ?(3), Z = 2, R = 0.0484. The geometry about the cadmium is octahedral with a square planar arrangement of the thf ligands and a fluorine from each (BF(4))(-) occupying the remaining two octahedral sites. Reactions of [Cd(2)(thf)(5)](BF(4))(4) with either HC(3,5-Me(2)pz)(3) or HC(3-Phpz)(3) yield the dicationic, homoleptic compounds {[HC(3,5-Me(2)pz)(3)](2)Cd}(BF(4))(2) (3) and {[HC(3-Phpz)(3)](2)Cd}(BF(4))(2) (4) (pz = 1-pyrazolyl). The solid state structure of 3 has been determined by X-ray crystallography. Crystal data: rhombohedral, R&thremacr;, a = 12.236(8) ?, c = 22.69(3) ?, V = 2924(4) ?(3), Z = 3, R = 0.0548. The cadmium is bonded to the six nitrogen donor atoms in a trigonally distorted octahedral arrangement. Four monocationic, mixed ligand tris(pyrazolyl)methane-tris(pyrazolyl)borate complexes {[HC(3,5-Me(2)pz)(3)][HB(3,5-Me(2)pz)(3)]Cd}(BF(4)) (5), {[HC(3,5-Me(2)pz)(3)][HB(3-Phpz)(3)]Cd}(BF(4)) (6), {[HC(3-Phpz)(3)][HB(3,5-Me(2)pz)(3)]Cd}(BF(4)) (7), and {[HC(3-Phpz)(3)][HB(3-Phpz)(3)]Cd}(BF(4)) (8) are prepared by appropriate conproportionation reactions of 3or 4 with equimolar amounts of the appropriate homoleptic neutral tris(pyrazolyl)borate complexes [HB(3,5-Me(2)pz)(3)](2)Cd or [HB(3-Phpz)(3)](2)Cd. Solution (113)Cd NMR studies on complexes 3-8 demonstrate that the chemical shifts of the new cationic, tris(pyrazolyl)methane complexes are very similar to the neutral tris(pyrazolyl)borate complexes that contain similar substitution of the pyrazolyl rings.     

Syntheses, reactivity and DFT studies of group 2 and group 12 metal complexes of tris(pyrazolyl)methanides featuring "free" pyramidal carbanions

Reactions of HC(Me2pz)3 with Grignard reagents, dialkyl magnesium compounds and dimethylzinc are reported, together with a DFT study on some of the aspects of this chemistry. Reactions of HC(Me2pz)3 with MeMgX (X=Cl or Br) gave the half-sandwich zwitterionic compounds [Mg((Me)Tpmd)X] (X=Cl (2) or Br (3); (Me)Tpmd(-)=[C(Me2pz)3](-)). Addition of HCl to 2 gave the structurally characterised half-sandwich compound [Mg{HC(Me2pz)3}Cl2(thf)] (4). The zwitterionic sandwich compound [Mg(MeTpmd)2] (5) formed in low yields in the reaction of MeMgX with HC(Me2pz)3 but was readily prepared from HC(Me2pz)3 and either MgnBu2 or MgPh2. The structurally characterised compound 5 contains two "naked" sp3-hybridised carbanions fully separated from the dicationic metal centre. Only by using MgPh2 as starting material could the half-sandwich compound [Mg(MeTpmd)Ph(thf)] (6) be isolated. The zwitterionic sandwich compound 5 reacted with HOTf (OTf(-)=[O3SCF3](-)) to form the dication [Mg{HC(Me2pz)3}2]2+ (7(2+)), which was structurally characterised. Pulsed field gradient spin-echo (PGSE) diffusion NMR spectroscopy revealed both compounds to be intact in solution. In contrast to the magnesium counterparts, HC(Me2pz)3 reacted only slowly with ZnMe2 (and not at all with ZnPh2) to form the half-sandwich zwitterion [Zn(MeTpmd)Me] (8), which contains a cationic methylzinc moiety separated from a single sp3-hybridised carbanion. Density functional calculations on the zwitterions [M(MeTpmd)Me] and [M(MeTpmd)2] (M=Mg, Zn) revealed that the HOMO in each case is a (Me)Tpmd-based carbanion lone pair. The kappa 1C isomers of [M(MeTpmd)Me] were calculated to be considerably less stable than their kappa 3N-bound counterparts, with the largest gain in energy for Mg due to the greater ease of electron transfer from metal to the (Me)Tpmd apical carbon atom on formation of the zwitterion. Moreover, the computed M-C bond dissociation enthalpies of the kappa 1C isomers of [M(MeTpmd)Me] are considerably higher than expected by simple extrapolation from the corresponding computed H-C bond dissociation enthalpy.     

Titanium tert-butoxyimido compounds

The synthesis and molecular and electronic structures of the first tert-butoxyimido complexes of titanium (TiNO(t)Bu functional group) are reported, featuring a variety of mono- or poly-dentate, neutral or anionic N-donor ligands. Reaction of Ti(NMe(2))(2)Cl(2) with (t)BuONH(2) gave good yields of Ti(NO(t)Bu)Cl(2)(NHMe(2))(2) (1). Compound 1 serves as an excellent entry point into new tert-butoxyimido complexes by reaction with a variety of fac-N(3) donor ligands, namely, Me(3)[9]aneN(3) (trimethyl-1,4,7-triazacyclononane), HC(Me(2)pz)(3) (tris(3,5-dimethylpyrazolyl)methane), or Me(3)[6]aneN(3) (trimethyl-1,3,5-triazacyclohexane) to give Ti(NO(t)Bu)(Me(3)[9]aneN(3))Cl(2) (2), Ti(NO(t)Bu){HC(Me(2)pz)(3)}Cl(2) (3), or Ti(NO(t)Bu)(Me(3)[6]aneN(3))Cl(2) (4) in good yield. It was found that 4 could be converted into Ti(NO(t)Bu)Cl(2)(py)(3) (5) in very good yield by reaction with an excess of pyridine. Compound 5 is effective in a range of salt metathesis reactions with lithiated amide or pyrrolide ligands, and reacts with Li(2)N(2)N(py), Li(2)N(2)N(Me), LiN(pyr)N(Me(2)), or Li(2)N(2)(pyr)N(Me) to give Ti(N(2)N(py))(NO(t)Bu)(py) (6), Ti(N(2)N(Me))(NO(t)Bu)(py) (7), Ti(N(pyr)N(Me(2)))(NO(t)Bu)Cl(py)(2) (9), or Ti(N(2)(pyr)N(Me))(NO(t)Bu)(py)(2) (10) in moderate to good yields (N(2)N(py) = (2-NC(5)H(4))C(Me)(CH(2)NSiMe(3))(2); N(2)N(Me) = MeN(CH(2)CH(2)NSiMe(3))(2); N(pyr)N(Me(2)) = Me(2)NCH(2)(2-NC(4)H(3)); N(2)(pyr)N(Me) = MeN{CH(2)(2-NC(4)H(3))}(2)). Compounds 7, 9, and 10 reacted with 2,2'-bipyridyl by pyridine exchange reactions forming Ti(N(2)N(Me))(NO(t)Bu)(bipy) (8), Ti(N(pyr)N(Me(2)))(NO(t)Bu)Cl(bipy) (11), and Ti(N(2)(pyr)N(Me))(NO(t)Bu)(bipy) (12). Ten tert-butoxyimido compounds, namely, 1-6, 11, and 12, have been structurally characterized revealing approximately linear Ti-N-O(t)Bu linkages with Ti-N distances [range 1.686(2)-1.734(2) ?] that are generally intermediate between those in the homologous alkylimido and phenylimido analogues, and shorter than in the diphenylhydrazido counterparts. Density functional theory (DFT) studies on the model compounds Ti(NR)Cl(2)(NHMe(2))(2) (1_R; R = OMe, Me, Ph, NMe(2)) confirmed this trend and found that the destabilizing effect of the -OMe oxygen 2p(π) lone pair on one of the Ti-N π-bonds in 1_OMe is comparable to that of the occupied phenyl ring π orbitals in the phenylimido homologue 1_Ph but much less than for the -NMe(2) nitrogen lone pair in 1_NMe(2).     

Bis‐ and Tris(pyrazolyl)borate/Methane‐Stabilized PIII‐Centered Cations

We report the synthesis of [H₂B(pz)₂PR]⁺, [H₂C(pz)₂PR]⁺², [HB(pz)₃P]⁺², and [HC(pz)₃P]⁺³ (H₂B(pz)₂=bis(pyrazolyl)borate; H₂C(pz)₂=bis(pyrazolyl)methane; HB(pz)₃=tris(pyrazolyl)borate; HC(pz)₃=tris(pyrazolyl) methane; R=Ph, Cy or Et₂N) by reaction of the corresponding neutral or anionic ligands with chlorophosphines in the presence of TMSOTf. The structures of these compounds were determined by X‐ray crystallographic analysis and the nature of their bonding was examined using density functional theory.     

Mononuclear, helical binuclear palladium and lithium complexes bearing a new pyrrole-based NNN-pincer ligand: fluxional property

A new pyrrole based NNN-pincer ligand, 2,5-bis(3,5-dimethylpyrazolylmethyl)pyrrole 2, was readily synthesized in two steps from pyrrole in 56% yield. The lithiation of the pincer ligand 2 using n-BuLi led to isolation of the dimeric lithium complex, [Li{μ-C(4)H(2)N-2,5-(CH(2)Me(2)pz)(2)-N,N,N}](2) 4, in 23% crystalline yield. The transmetalation reaction of 4 with [Pd(PhCN)(2)Cl(2)] afforded the mononuclear Pd(II) complex, [PdCl{C(4)H(2)N-2,5-(CH(2)Me(2)pz)(2)-N,N,N}] 5, containing one chloride ion in 45% yield. Alternatively 5 was obtained in an excellent yield of 87% by the reaction 2 of with [Pd(COD)Cl(2)] in the presence of triethylamine. On the contrary, a 20-membered macrometalacyclic molecule, [Pd(2)Cl(4){μ-C(4)H(3)N-2,5-(CH(2)Me(2)pz)(2)-N,N}(2)] 6, in which two PdCl(2) units are bridged by two molecules of 2 to give a helical structure, was synthesized by the reaction of 2 with [Pd(COD)Cl(2)] in the absence of base. The acetate analogue of complex 5, [Pd(OAc){C(4)H(2)N-2,5-(CH(2)Me(2)pz)(2)-N,N,N}] 3, was obtained by the treatment of 2 with [Pd(OAc)(2)]. The pyrrole twist angle of 5 is higher than that of 3. Complexes 3 and 5 show an AB pattern for their methylene protons at room temperature in CDCl(3) as well as in DMSO-d(6). The variable temperature NMR studies showed that the acetate and chloride complexes exhibit slightly different coalescence temperatures, which is a solvent dependent phenomenon, and twist angles.     

Synthesis and reactivity of uranium(IV) amide complexes supported by a triamidotriazacyclononane ligand

Reaction of [U{(SiMe2NPh)3-tacn}Cl] with LiNEt2 or LiNPh2 affords the corresponding amide compounds, [U{(SiMe2NPh)3-tacn}(NR2)] (R = Et (1), R = Ph (2)). The complexes have been fully characterized by spectroscopic methods and the solid-state structure of 1 was determined by single-crystal X-ray diffraction analysis. The six nitrogen atoms of the tris(dimethylsilylanilide)triazacyclononane ligand are in a trigonal prismatic configuration with the nitrogen atom of the diethylamide ligand capping one of the trigonal faces of the trigonal prism. Crystallization of 2 from CH3CN solution gave crystals of the six-membered heterocycle [U{(SiMe2NPh)3-tacn}{kappa2-(HNC(Me))2CC[triple bond]N}] (3). The reactivity of the amides was investigated. Both compounds undergo acid-base reactions with protic substrates such as HOC6H2-2,4,6-Me3, 3,5-Me2pzH (pz = pyrazolyl) and HSC5H4N to give the corresponding [U{(SiMe2NPh)3-tacn}X] (X = OC6H2-2,4,6-Me3 (4), 3,5-Me2pzH (5), kappa2-SC5H4N (6)) complexes. The solid-state structures of and were determined by single-crystal X-ray diffraction and revealed that the compounds are eight-coordinate with dodecahedral geometry.     

Modular approach to tridentate N,O,N' ligands using pyrazolylborate chemistry

Two anionic tridentate N,O,N' chelators, [pz(Ph)B(mu-pz)(mu-O)B(Ph)pz](-) (3(-)) and [pz(Ph)(Ph)B(mu-pz)(mu-O)B(Ph)pz(Ph)](-) (4(-)), as well as the corresponding complexes [Fe(3)(py)Cl], [Fe(3)Cl(2)] and [Cu(3)Cl], have been synthesised and structurally characterised by X-ray crystallography (pz: pyrazolyl, pz(Ph): 3-phenylpyrazolyl, py: pyridine). Since our synthesis approach takes advantage of the highly modular pyrazolylborate chemistry, inexpensive and relatively resistant N,O,N' ligands of varying steric demand are readily accessible. The complexes [Fe(3)(py)Cl] and [Fe(3)Cl(2)] possess a distorted trigonal-bipyramidal configuration with the pyrazolyl rings occupying equatorial positions and the oxygen donor being located at an apical position. The complex [Cu(3)Cl] crystallises as chloro-bridged dimers featuring Cu(II) ions with ligand environments that are intermediate between a square-planar and a trigonal-bipyramidal geometry.     

Synthesis, structures, and olefin polymerization capability of vanadium(4+) imido compounds with fac-N3 donor ligands

One-pot reactions of V(NMe2)4 with a range of primary alkyl- and arylamines RNH2 and Me3SiCl afforded the corresponding five-coordinate vanadium(4+) imido compounds V(NR)Cl2(NHMe2)2 [R = 2,6-C6H3(i)Pr2 (1a, previously reported), 2-C6H4(t)Bu (1b), 2-C6H4CF3 (1c), (t)Bu (1d), Ad (Ad = adamantyl, 1e)]. The crystal structures of 1b (two diamorphic forms) and 1c featured N-H...Cl hydrogen-bonded chains. Reaction of 1a-e with the neutral face-capping, N3 donor ligands TACN (TACN = 1,4,7-trimethyltriazacyclononane) or TPM [TPM = tris(3,5-dimethylpyrazolyl)methane] gave the corresponding six-coordinate complexes V(NR)(TACN)Cl2 (2a-e) and V(NR)(TPM)Cl2 (3a-e). The X-ray structures of 2b, 2c, 2d, 3b, 3c, and 3e were determined. When activated with methylaluminoxane, certain of the complexes V(NR)(TPM)Cl2 (3) formed moderately active ethylene polymerization catalysts, whereas none of the compounds V(NR)(TACN)Cl2 (2) were active.     

Solid state and solution structures of rhodium and iridium poly(pyrazolyl)borate diene complexes

The structures adopted by a range of poly(pyrazolyl)borate complexes [ML2Tp(x)] [M = Rh, Ir; L2 = diene; Tp(x) = Bp' {dihydrobis(3,5-dimethylpyrazolyl)borate}, Tp' {hydrotris(3,5-dimethylpyrazolyl)borate}, Tp {hydrotris(pyrazolyl)borate}, B(pz)4 {tetrakis(pyrazolyl)borate}] have been investigated. Low steric hindrance between ligands in [Rh(eta-nbd)Tp] (nbd = norbornadiene), [Rh(eta-cod)Tp] (cod = cycloocta-1,5-diene) and [Rh(eta-nbd)Tp'] results in K3 coordination of the pyrazolylborate but [M(eta-cod)Tp'] (M = Rh, Ir) are kappa2 coordinated with the free pyrazolyl ring positioned above and approximately parallel to the square plane about the metal. All but the most sterically hindered Tp(x) complexes undergo fast exchange of the coordinated and uncoordinated pyrazolyl rings on the NMR spectroscopic timescale. For [Rh(eta-cod){B(pz)4}], [Rh(eta-dmbd)Tp'] (dmbd = 2,3-dimethylbuta-1,3-diene) and [Rh(eta-cod)Tp(Ph)] {Tp(Ph) = hydrotris(3-phenylpyrazolyl)borate} the fluxional process is slowed at low temperatures so that inequivalent pyrazolyl rings are observed. The bonding modes of the Tp' ligand (but not of other pyrazolylborate ligands) can be determined by 11B NMR and IR spectroscopy. The 11B chemical shifts (for a series of Tp' complexes) show the general pattern, kappa3 < -7.5 ppm < kappa2 and the nu(BH) stretch kappa3 > 2500 cm(-1) > kappa2. The electrochemical behaviour of the pyrazolylborate complexes is related to the degree of structural change which occurs on electron transfer. One-electron oxidation of complexes with Tp', Tp and B(pz)4 ligands is generally reversible although that of [Ir(etacod)Tp] is only reversible at higher scan rates and that of [Ir(eta-cod){B(pz)4}] is irreversible. Of the complexes with the more sterically hindered Tp(Ph) ligand, only [Rh(eta-nbd)Tp(Ph)] shows any degree of reversible oxidation. The ESR spectra of a range of Rh(II) complexes show coupling to both 14N and 103Rh nuclei in most cases but what appears to be coupling to rhodium and one hydrogen atom, possibly a hydride ligand, for the oxidation product of [Rh(eta-nbd)Tp(Ph)].     

Ammonolysis of mono(pentamethylcyclopentadienyl) titanium(IV) derivatives

Ammonolyses of mono(pentamethylcyclopentadienyl) titanium(IV) derivatives [Ti(eta5-C5Me5)X3] (X = NMe2, Me, Cl) have been carried out in solution to give polynuclear nitrido complexes. Reaction of the tris(dimethylamido) derivative [Ti(eta5-C5Me5)(NMe2)3] with excess of ammonia at 80-100 degrees C gives the cubane complex [[Ti(eta5-C5Me5)]4(mu3-N)4] (1). Treatment of the trimethyl derivative [Ti(eta5-C5Me5)Me3] with NH3 at room temperature leads to the trinuclear imido-nitrido complex [[Ti(eta/5-CsMes)(mu-NH)]3(mu3-N)] (2) via the intermediate [[Ti(eta5-C5Me5)Me]2(mu-NH)2] (3). The analogous reaction of [Ti(eta5-C5Me5)Me3] with 2,4,6-trimethylaniline (ArNH2) gives the dinuclear imido complex [[Ti(eta5-C5Me5)Me])2(mu-NAr)2] (4) which reacts with ammonia to afford [[Ti(eta5-C5Me5)(NH2)]2(mu-NAr)2] (5). Complex 2 has been used, by treatments with the tris(dimethylamido) derivatives [Ti(eta5-C5H5-nRn)(NMe2)3], as precursor of the cubane nitrido systems [[Ti4(eta5-C5Me5)3(eta5-C5H5-nRn)](mu3-N)4] [R = Me n = 5 (1), R = H n = 0 (6), R = SiMe3 n = 1 (7), R = Me n = 1 (8)] via dimethylamine elimination. Reaction of [Ti(eta5-C5Me5)Cl3] or [Ti(eta5-C5Me5)(NMe2)Cl2] with excess of ammonia at room temperature gives the dinuclear complex [[Ti2(eta5-C5Me5)2Cl3(NH3)](mu-N)] (9) where an intramolecular hydrogen bonding and a nonlineal nitrido ligand bridge the "Ti(eta5-C5Me5)Cl(NH3)" and "Ti(eta5-C5Me5)Cl2" moieties. The molecular structures of [[Ti(eta5-C5Me5)Me]2 (mu-NAr)2] (4) and [[Ti2(eta5-C5Me5)2Cl3(NH3)](mu-N)] (9) have been determined by X-ray crystallographic studies. Density functional theory calculations also have been conducted on complex 9 to confirm the existence of an intramolecular N-H...Cl hydrogen bond and to evaluate different aspects of its molecular disposition.     

Synthesis, reactivity, spectroscopic characterization, X-ray structures, PGSE, and NOE NMR studies of (eta5-C5Me5)-rhodium and -iridium derivatives containing bis(pyrazolyl)alkane ligands

Rhodium(III) and iridium(III) complexes containing bis(pyrazolyl)methane ligands (pz = pyrazole, L' in general; specifically, L1 = H2C(pz)2, L2 = H2C(pzMe2)2, L3 = H2C(pz4Me)2, L4 = Me2C(pz)2), have been prepared in a study exploring the reactivity of these ligands toward [Cp*MCl(mu-Cl)]2 dimers (M = Rh, Ir; Cp* = pentamethylcyclopentadienyl). When the reaction was carried out in acetone solution, complexes of the type [Cp*M(L')Cl]Cl were obtained. However, when L1 and L2 ligands have been employed with excess [Cp*MCl(mu-Cl)]2, the formation of [Cp*M(L')Cl][Cp*MCl3] species has been observed. PGSE NMR measurements have been carried out for these complexes, in which the counterion is a cyclopentadienyl metal complex, in CD2Cl2 as a function of the concentration. The hydrodynamic radius (rH) and, consequently, the hydrodynamic volume (VH) of all the species have been determined from the measured translational self-diffusion coefficients (Dt), indicating the predominance of ion pairs in solution. NOE measurements and X-ray single-crystal studies suggest that the [Cp*MCl3]- approaches the cation, orienting the three Cl-legs of the "piano-stool" toward the CH2 moieties of the bis(pyrazolyl)methane ligands. The reaction of 1 equiv of [Cp*M(L')Cl]Cl or [Cp*M(L')Cl][Cp*MCl3] with 1 equiv of AgX (X = ClO4 or CF3SO3) in CH2Cl2 allows the generation of [Cp*M(L')Cl]X, whereas the reaction of 1 equiv of [Cp*M(L')Cl] with 2 equiv of AgX yields the dicationic complexes [Cp*M(L')(H2O)][X]2, where single water molecules are directly bonded to the metal atoms. The solid-state structures of a number of complexes were confirmed by X-ray crystallographic studies. The reaction of [Cp*Ir(L')(H2O)][X]2 with ammonium formate in water or acetone solution allows the generation of the hydride species [Cp*Ir(L')H][X].