Atomic carbon as a terminal ligand: studies of a carbidomolybdenum anion featuring solid-state (13)C NMR data and proton-transfer self-exchange kinetics.

Anion [CMo(N[R]Ar)(3)](-) (R = C(CD(3))(2)CH(3) or (t)Bu, Ar = 3,5-C(6)H(3)Me(2)) containing one-coordinate carbon as a terminal substituent and related molecules have been studied by single-crystal X-ray crystallography, solution and solid-state (13)C NMR spectroscopy, and density functional theory (DFT) calculations. Chemical reactivity patterns for [CMo(N[R]Ar)(3)](-) have been investigated, including the kinetics of proton-transfer self-exchange involving HCMo(N[R]Ar)(3), the carbidomolybdenum anion's conjugate acid. While the Mo triple bond C bond lengths in [K(benzo-15-crown-5)(2)][CMo(N[R]Ar)(3)] and the parent methylidyne, HCMo(N[R]Ar)(3), are statistically identical, the carbide chemical shift of delta 501 ppm is much larger than the delta 282 ppm shift for the methylidyne. Solid-state (13)C NMR studies show the carbide to have a much larger chemical shift anisotropy (CSA, 806 ppm) and smaller (95)Mo--(13)C coupling constant (60 Hz) than the methylidyne (CSA = 447 ppm, (1)J(MoC) = 130 Hz). DFT calculations on model compounds indicate also that there is an increasing MoC overlap population on going from the methylidyne to the terminal carbide. The pK(a) of methylidyne HCMo(N[R]Ar)(3) is approximately 30 in THF solution. Methylidyne HCMo(N[R]Ar)(3) and carbide [CMo(N[R]Ar)(3)](-) undergo extremely rapid proton-transfer self-exchange reactions in THF, with k = 7 x 10(6) M(-1) s(-1). Besides being a strong reducing agent, carbide [CMo(N[R]Ar)(3)](-) reacts as a nucleophile with elemental chalcogens to form carbon-chalcogen bonds and likewise reacts with PCl(3) to furnish a carbon-phosphorus bond.     

Complexes of an anionic gallium(I) N-heterocyclic carbene analogue with group 14 element(II) fragments: synthetic, structural and theoretical studies

The reactions of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue, [K(tmeda)][:Ga{[N(Ar)C(H)]2}], Ar = C6H3Pri2-2,6, with the heavier group 14 alkene analogues, R2E=ER2, E = Ge or Sn, R = -CH(SiMe3)2, have been carried out. In 2:1 stoichiometries, these lead to the ionic [K(tmeda)][R2EGa{[N(Ar)C(H)]2}] complexes which exhibit long E-Ga bonds. The nature of these bonds has been probed by DFT calculations, and the complexes have been compared to neutral NHC adducts of group 14 dialkyls. The 4:1 reaction of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with R2Sn=SnR2 leads to the digallyl stannate complex, [K(tmeda)][RSn[Ga{[N(Ar)C(H)]2}]2], presumably via elimination of KR. In contrast, the reaction of the gallium heterocycle with PbR2 affords the digallane4, [Ga{[N(Ar)C(H)]2}]2, via an oxidative coupling reaction. For sake of comparison, the reactions of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with Ar'2E=EAr'2, E = Ge, Sn or Pb, Ar' = C6H2Pri3-2,4,6, were carried out and led to either no reaction (E = Ge), the formation of [K(tmeda)][Ar'2SnGa{[N(Ar)C(H)]2}] (E = Sn), or the gallium(III) heterocycle, [Ar'Ga{[N(Ar)C(H)]2}] (E = Pb). Salt elimination reactions between [K(tmeda)][:Ga{[N(Ar)C(H)]2}] and the guanidinato group 14 complexes [(Giso)ECl], E = Ge or Sn, Giso = [Pri2NC{N(Ar)}2]-, gave the neutral [(Giso)EGa{[N(Ar)C(H)]2}] complexes. All complexes have been characterized by NMR spectroscopy and X-ray crystallographic studies.     

A nitridoniobium(V) reagent that effects acid chloride to organic nitrile conversion: synthesis via heterodinuclear (Nb/Mo) dinitrogen cleavage, mechanistic insights, and recycling

The transformation of acid chlorides (RC(O)Cl) to organic nitriles (RC[triple bond]N) by the terminal niobium nitride anion [N[triple bond]Nb(N[Np]Ar)3]- ([1a-N]-, where Np = neopentyl and Ar = 3,5-Me2C6H3) via isovalent N for O(Cl) metathetical exchange is presented. Nitrido anion [1a-N]- is obtained in a heterodinuclear N2 scission reaction employing the molybdenum trisamide system, Mo(N[R]Ar)3 (R = t-Bu, 2a; R = Np, 2b), as a reaction partner. Reductive scission of the heterodinuclear bridging N2 complexes, (Ar[R]N)3Mo-(mu-N2)Nb(N[Np]Ar)3 (R = t-Bu, 3b; R = Np, 3c) with sodium amalgam provides 1 equiv each of the salt Na[1a-N] and neutral N[triple bond]Mo(N[R]Ar)3 (R = t-Bu, 2a-N; R = Np, 2b-N). Separation of 2-N from Na[1a-N] is readily achieved. Treatment of salt Na[1a-N] with acid chloride substrates in tetrahydrofuran (THF) furnishes the corresponding organic nitriles concomitant with the formation of NaCl and the oxo niobium complex O[triple bond]Nb(N[Np]Ar)3 (1a-O). Utilization of 15N-labeled 15N2 gas in this chemistry affords a series of 15N-labeled organic nitriles establishing the utility of anion [1a-N]- as a reagent for the 15N-labeling of organic molecules. Synthetic and computational studies on model niobium systems provide evidence for the intermediacy of both a linear acylimido and niobacyclobutene species along the pathway to organic nitrile formation. High-yield recycling of oxo 1a-O to a niobium triflate complex appropriate for heterodinuclear N2 scission has been developed. Specifically, addition of triflic anhydride (Tf2O, where Tf = SO2CF3) to an Et2O solution of 1a-O provides the bistriflate complex, Nb(OTf)2(N[Np]Ar)3 (1a-(OTf)2), in near quantitative yield. One-electron reduction of 1a-(OTf)2 with either cobaltocene (Cp2Co) or Mg(THF)3(anthracene) provided the monotriflato complex, Nb(OTf)(N[Np]Ar)3 (1a-(OTf)), which efficiently regenerates complexes 3b and 3c when treated with the molybdenum dinitrogen anions [N2Mo(N[t-Bu]Ar)3]- ([2a-N2]-) or [N2Mo(N[Np]Ar)3]- ([2b-N2]-), respectively.     

Synthesis and structural characterisation of group 10 metal(II) gallyl complexes: analogies with platinum diboration catalysts?

Reactions of the anionic gallium(i) heterocycle, [:Ga{[N(Ar)C(H)](2)}](-) (Ar = C(6)H(3)Pr(i)(2)-2,6), with a variety of mono- and bidentate phosphine, tmeda and 1,5-cyclooctadiene (COD) complexes of group 10 metal dichlorides are reported. In most cases, salt elimination occurs, affording either mono(gallyl) complexes, trans-[MCl{Ga{[N(Ar)C(H)](2)}}(PEt(3))(2)] (M = Ni or Pd) and cis-[PtCl{Ga{[N(Ar)C(H)](2)}}(L)] (L = R(2)PCH(2)CH(2)PR(2), R = Ph (dppe) or cyclohexyl (dcpe)), or bis(gallyl) complexes, trans-[M{Ga{[N(Ar)C(H)](2)}}(2)(PEt(3))(2)] (M = Ni, Pd or Pt), cis-[Pt{Ga{[N(Ar)C(H)](2)}}(2)(PEt(3))(2)], cis-[M{Ga{[N(Ar)C(H)](2)}}(2)(L)] (M = Ni, Pd or Pt; L = dppe, Ph(2)CH(2)PPh(2) (dppm), tmeda or COD). The crystallographic and spectroscopic data for the complexes show that the trans-influence of the gallium(i) heterocycle lies in the series, B(OR)(2) > H(-) > PR(3) approximately [:Ga{[N(Ar)C(H)](2)}](-) > Cl(-). Comparisons between the reactivity of one complex, [Pt{Ga{[N(Ar)C(H)](2)}}(2)(dppe)], with that of closely related platinum bis(boryl) complexes indicate that the gallyl complex is not effective for the catalytic or stoichiometric gallylation of alkenes or alkynes. The phosphaalkyne, Bu(t)C[triple bond, length as m-dash]P, does, however, insert into one gallyl ligand of the complex, leading to the novel, crystallographically characterised P,N-gallyl complex, [Pt{Ga{[N(Ar)C(H)](2)}}{Ga{PC(Bu(t))C(H)[N(Ar)]C(H)N(Ar)}}(dppe)]. An investigation into the mechanism of this insertion reaction has been undertaken.     

Reactions of tris(amino)phosphines with arylsulfonyl azides: product dependency on tris(amino)phosphine structure

The Staudinger reaction of N(CH2CH2NR)3P [R = Me (1), Pr (2)] with 1 equiv of N3SO2C6H4Me-4 gave the ionic phosphazides [N(CH2CH2NR)3PN][SO2C6H4Me-4] [R = Me (3), R = Pr (5a)], and the same reaction of 2 with N3SO2C6H2Me3-2,4,6 gave the corresponding aryl sulfinite 5b. On the other hand, the reaction of 1 with 0.5 equiv of N3SO2Ar (Ar = C6H4Me-4) furnished the novel ionic phosphazide [[N(CH2CH2NMe)3P]2(mu-N3)][SO2Ar] (6). Data that shed light on the mechanistic pathway leading to 3 were obtained by low temperature 31P NMR spectroscopy. A crystal and molecular structure analysis of the phosphazide sulfonate [N(CH2CH2NMe)3PN3][SO3C6H4Me-4] (4), obtained by atmospheric oxidation of 3, indicated an ionic structure, the cationic part of which is stabilized by a transannular P-N bond. A crystal and molecular structure analysis of 6 also indicated an ionic structure in which the cation features two untransannulated N(CH2CH2NMe)3P cages bridged by an azido group in an eta 1: mu: eta 1 fashion. The reaction of P(NMe2)3 with N3SO2Ar (Ar = C6H4Me-4) in a 1:0.5 molar ratio furnished [[(Me2N)3P]2(mu-N3)][SO2-Ar] (11) in quantitative yield. On the other hand, the same reaction involving a 1:1 molar ratio of P(NMe2)3 and N3SO2Ar produced a mixture of 11, [(Me2N)3PN3][SO2Ar] (12), and the iminophosphorane (Me2N)3P=NSO2Ar (10). In contrast, the bicyclic tris(amino)phosphines MeC(CH2NMe)3P (7) and O=P(CH2NMe)3P (8) reacted with N3SO2-Ar (Ar = C6H4Me-4) to give the iminophosphorane MeC(CH2NMe)3P=NSO2Ar (14) (structured by X-ray means) and O=P(CH2NMe)3P=NSO2Ar (16) via the intermediate phosphazides MeC(CH2NMe)3PN3SO2Ar (13) and O=P(CH2NMe)3PN3SO2Ar (15), respectively. The variety of products obtained from the reactions of arylsulfonyl azides with proazaphosphatranes (1 and 2), acyclic P(NMe2)3, bicyclic tris(amino)phosphines 7 and 8 are rationalized in terms of steric and basicity variations among the phosphorus reagents.     

Complexes of a gallium heterocycle with transition metal dicyclopentadienyl and cyclopentadienylcarbonyl fragments, and with a dialkylmanganese compound

The reactivity of several transition metal half sandwich complexes towards an anionic gallium(I) heterocyclic complex, [K(tmeda)][Ga{[N(Ar)C(H)]2}](Ar = C6H3Pri2-2,6), has been investigated. This has led to the anionic half sandwich complexes, [K(tmeda)][(C5H4R)M(CO)n[Ga{[N(Ar)C(H)]2}]](M = V, R = H, n= 3; M = Mn, R = Me, n= 2; M = Co, R = H, n= 1), which crystallographic studies show to form dimers (M = Mn and Co) or a polymer (M = V) through bridging potassium cations. The metal-gallium bond lengths in all complexes are very short which, combined with some spectroscopic evidence, is suggestive of M-Ga pi-bonding. Density functional theory studies of models of all complexes indicate that the level of back-bonding in these complexes is, however, minimal and of a similar order to that seen in analogous complexes incorporating neutral N-heterocyclic carbene ligands. Reactions of the metallocenes, [M(C5H4Me)2](M = V or Cr), with the digallane4, [Ga{[N(Ar)C(H)]2}]2, have afforded the neutral complexes, [M(C5H4Me)2[Ga{[N(Ar)C(H)]2}]], which are thought to be formed via an initial oxidative insertion of the transition metal centre into the Ga-Ga bond of the digallane. X-Ray crystallography shows the complexes to be monomeric. One (M = V) reacts with one equivalent of [K(tmeda)][Ga{[N(Ar)C(H)]2}] to give the crystallographically characterised, anionic bis(gallyl)-complex, [K(tmeda)][V(C5H4Me)2[Ga{[N(Ar)C(H)]2}]2]. For comparison, the reaction of [K(tmeda)][Ga{[N(Ar)C(H)]2}] with [Mn{CH(SiMe3)2}2] was carried out and gave the monomeric, anionic complex, [K(tmeda)][Mn{CH(SiMe3)2}2[Ga{[N(Ar)C(H)]2}]].     

Optimizing small molecule activation and cleavage in three-coordinate M[N(R)Ar]3 complexes

The sterically hindered, three-coordinate metal systems M[N(R)Ar]3 (R = tBu, iPr; Ar = 3,5-C6H3Me2) are known to bind and activate a number of fundamental diatomic molecules via a [Ar(R)N]3M-L-L-M[N(R)Ar]3 dimer intermediate. To predict which metals are most suitable for activating and cleaving small molecules such as N(2), NO, CO, and CN(-), the M-L bond energies in the L-M(NH2)3 (L = O, N, C) model complexes were calculated for a wide range of metals, oxidation states, and dn (n = 2-6) configurations. The strongest M-O, M-N, and M-C bonds occurred for the d2, d3, and d4 metals, respectively, and for these d(n) configurations, the M-C and M-O bonds were calculated to be stronger than the M-N bonds. For isoelectronic metals, the bond strengths were found to increase both down a group and to the left of a period. Both the calculated N-N bond lengths and activation barriers for N2 bond cleavage in the (H2N)3M-N-N-M(NH2)3 intermediate dimers were shown to follow the trends in the M-N bond energies. The three-coordinate complexes of Ta(II), W(III), and Nb(II) are predicted to deliver more favorable N2 cleavage reactions than the experimentally known Mo(III) system and the Re(III)Ta(III) dimer, [Ar(R)N]3Re-CO-Ta[N(R)Ar]3, is thermodynamically best suited for cleaving CO.     

A convenient synthesis of new isolable phosphaalkenes using the base-induced rearrangement of secondary vinylphosphines

The secondary vinylphosphines Ar(F)P(H)C(R)[double bond]CH(2) [2a, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = CH(3); 2b, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = C(6)H(5); 2c, Ar(F) = 2,4,6-(CF(3))(3)C(6)H(2), R = CH(3)] were prepared by treating the corresponding dichlorophosphine Ar(F)PCl(2) (1) with H(2)C[double bond]C(R)MgBr. In the presence of catalytic base (DBU or DABCO) the vinylphosphines (2a-c) undergo quantitative 1,3-hydrogen migration over 3 d to give stable and isolable phosphaalkenes Ar(F)P=C(R)CH(3) (3a, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = CH(3); 3b, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = C(6)H(5); 3c, Ar(F) = 2,4,6-(CF(3))(3)C(6)H(2), R = CH(3)). Under analogous conditions, only 90% conversion is observed in the base-catalyzed rearrangement of MesP(H)C(CH(3))[double bond]CH(2) to MesP[double bond]C(CH(3))(2). Presumably, the increase in acidity of the P-H group when electron-withdrawing groups are employed (i.e. 2a-c) favors quantitative rearrangement to the phosphaalkene tautomer (3a-c). Thus, the double-bond migration reaction is a convenient and practical method of preparing new phosphaalkenes with C-methyl substituents.     

Cationic Rh complexes with novel spiro tetraarylpentaborate anions prepared from arylboronic acids and aryloxorhodium complexes

Ar-B(OH)2 (1a: Ar = C6H4OMe-4, 1b: Ar = C6H3Me2-2,6) react immediately with Rh(OC6H4Me-4)(PMe3)3 (2) in 5 : 1 molar ratio at room temperature to generate [Rh(PMe3)4]+[B5O6Ar4]- (3a: Ar = C6H4OMe-4, 3b: Ar = C6H3Me2-2,6). p-Cresol (92%/Rh), anisole (80%/Rh) and H2O (364%/Rh) are formed from 1a and 2. The reaction of 1a with 2 for 24 h produces [Rh(PMe3)4]+[B5O6(OH)4]- (4) as a yellow solid. This is attributed to hydrolytic dearylation of once formed 3a because the direct reaction of 3a with excess H2O forms 4. An equimolar reaction of 2 with phenylboroxine (PhBO)3 causes transfer of the 4-methylphenoxo ligand from rhodium to boron to produce [Rh(PMe3)4]+[B3O3Ph3(OC6H4Me-4)]- (5). Arylboronic acids 1a and 1b react with Rh(OC6H4Me-4)(PR3)3 (6: R = Et, 8: R = Ph) and with Rh(OC6H4Me-4)(cod)(PR3) (11: R = iPr, 12: R = Ph) to form [Rh(PR3)4]+[B5O6Ar4]- (7a: R = Et, Ar = C6H4OMe-4, 7b: R = Et, Ar = C6H3Me2-2,6, 9a: R = Ph, Ar = C6H3Me2-2,6) and [Rh(cod)(PR3)(L)]+[B5O6Ar4]- (13b: R = iPr, L = acetone, Ar = C6H3Me2-2,6, 14a: R = Ph, L = PPh3, Ar = C6H4OMe-4, 14b: R = Ph, L = PPh3, Ar = C6H3Me2-2,6), respectively. Hydrolysis of 14a yields [Rh(cod)(PPh3)2]+[B5O6(OH)4]- (15) quantitatively.     

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.     

Synthesis, characterization, and reaction of aluminum halide amides supported by a bulky beta-diketiminato ligand

Monomeric aluminum chloride amides with the general formula LAl(Cl)NR2 (1, R = Me; 2, R = iPr; 3, R = SiMe 3; L = HC[C(Me)N(Ar)]2; Ar = 2,6- iPr2C6H3) were prepared by selected routes. Treatment of LAlBr 2 (4) and LAlI2 with LiNMe2 yielded LAl(Br)NMe2 (5) and LAl(I)NMe2 (6), respectively. The alkylation of 1 and 2 with MeLi gave the corresponding methylated compounds LAl(Me)NR2 (7, R = Me; 8, R = iPr); however, no reaction of 3 with MeLi was observed because of steric hindrance. Subsequent fluorination of 1- 3 afforded LAl(F)NR2 (9, R = Me; 10, R = iPr; 11, R = SiMe3). Compounds 1-11 were characterized by multinuclear NMR, electron impact mass spectrometry, and IR. The constitution of compounds 1-3 was confirmed by single-crystal X-ray diffraction studies.     

Four-coordinate phosphinidene complexes of titanium prepared by alpha-H-migration: phospha-Staudinger and phosphaalkene-insertion reactions

alpha-Hydrogen migration in the phosphide (Nacnac)Ti=CHtBu(PHR) (Nacnac- = [Ar]NC(Me)CHC(Me)N[Ar], Ar = 2,6-iPr2C6H3, R = C6H11, 2,4,6-iPr3C6H2, 2,4,6-tBuC6H2), prepared from salt metathesis of (Nacnac)Ti=CHtBu(PHR) with LiPHR, generates terminal and four-coordinate phosphinidene complexes (Nacnac)Ti=PR(CH2tBu), one of which was structurally characterized (R = 2,4,6-tBu3C6H2). Phosphinidene intermediate (Nacnac)Ti=PR(CH2tBu) (R = C6H11, 2,4,6-iPr3C6H2) transform to ([Ar]NC(Me)CHC(Me)P[R][CH2tBu])Ti=NAr(OEt2) through "phospha-Staudinger" and subsequent phosphaalkene-insertion reactions.     

Synthesis and structures of selected triazapentadienate of Li, Mn, Fe, Co, Ni, Cu(I), and Cu(II) using 2,4-N,N'-disubstituted 1,3,5-triazapentadienate anions as ancillary ligands: [N(Ar)C(NMe2)NC(NMe2)N(R)](-) (Ar = Ph, 2,6-(i)Pr2-C6H3; R = H, SiMe3)

Addition reaction of ArN(SiMe 3)M (Ar = Ph or 2,6 - (i) Pr 2-C 6H 3 (Dipp); M = Li or Na) to 2 equivalents of alpha-hydrogen-free nitrile RCN (R = dimethylamido) gave the dimeric [M{N(Ar)C(NMe 2)NC(NMe 2)N(SiMe 3)}] 2 ( 1a, Ar = Ph, M = Li; 1b, Ar = Ph, M = Na; 1c, Ar = Dipp, M = Li). 1d was obtained by hydrolysis of 1c at ambient temperature. Treatment of a double ratio of 1a or 1b with anhydrous MCl 2 (M = Mn, Fe, Co) yielded the 1,3,5-triazapentadienato complexes [M{N(Ph)C(NMe 2)NC(NMe 2)N(SiMe 3)} 2] (M = Mn, 2; Fe, 3; Co, 4) and with NiCl 2.6H 2O gave [M{N(Ph)C(NMe 2)NC(NMe 2)N(H)} 2] (M = Ni, 5). Treatment of an equiv of 1c with anhydrous CuCl in situ and in air led to complexes [{N(Dipp)C(NMe 2)NC(NMe 2)N(SiMe 3)}CuPPh 3] 6 and [Cu{N(Dipp)C(NMe 2)NC(NMe 2)N(H)} 2] 7, respectively. 1c, 1d, and 2- 7 were characterized by X-ray crystallography and microanalysis. 1c, 1d, 5, and 6 were well characterized by (1)H, (13)C NMR, 1c by (7)Li, and 6 by (31)P NMR as well. The structural features of these complexes were described in detail.     

Extremely bulky amido-group 14 element chloride complexes: potential synthons for low oxidation state main group chemistry

The preparation of a series of extremely bulky secondary amines, Ar*N(H)SiR(3) (Ar* = C(6)H(2){C(H)Ph(2)}(2)Me-2,6,4; R(3) = Me(3), MePh(2) or Ph(3)) is described. Their deprotonation with either LiBu(n), NaH or KH yields alkali metal amide complexes, several monomeric examples of which, [Li(L){N(SiMe(3))(Ar*)}] (L = OEt(2) or THF), [Na(THF)(3){N(SiMe(3))(Ar*)}] and [K(OEt(2)){N(SiPh(3))(Ar*)], have been crystallographically characterised. Reactions of the lithium amides with germanium, tin or lead dichloride have yielded the first structurally characterised two-coordinate, monomeric amido germanium(II) and tin(II) chloride complexes, [{(SiR(3))(Ar*)N}ECl] (E = Ge or Sn; R = Me or Ph), and a chloride bridged amido-lead(II) dimer, [{[(SiMe(3))(Ar*)N]Pb(μ-Cl)}(2)]. DFT calculations on [{(SiMe(3))(Ar*)N}GeCl] show its HOMO to exhibit Ge lone pair character and its LUMO to encompass its Ge based p-orbital. A series of bulky amido silicon(IV) chloride complexes have also been prepared and several examples, [{(SiR(3))(Ar*)N}SiCl(3)] (R(3) = Me(3), MePh(2)) and [{(SiMe(3))(Ar*)N}SiHCl(2)], were crystallographically characterised. The sterically hindered group 14 complexes reported in this study hold significant potential as precursors for kinetically stabilised low oxidation state and/or low coordination number group 14 complexes.     

Remarkable reactions of cyclooctatetraene diiron-bridging carbyne complexes with amino and amido compounds: nucleophilic addition to and breaking of the cyclooctatetraene ring

The reactions of the cationic, diiron-bridging carbyne complexes [Fe(2)(mu-CAr)(CO)(4)(eta(8)-C(8)H(8))]BF(4) (1, Ar=C(6)H(5); 2, Ar=p-CH(3)C(6)H(4); 3, Ar=p-CF(3)C(6)H(4)) with LiN(C(6)H(5))(2) in THF at low temperature gave novel N-nucleophilic-addition products, namely, the neutral, diiron-bridging carbyne complexes [Fe(2)(mu-CAr)(CO)(4)(eta(7)-C(8)H(8)N(C(6)H(5))(2))] (4, Ar=C(6)H(5); 5, Ar=p-CH(3)C(6)H(4); 6, Ar=p-CF(3)C(6)H(4))). Cationic bridging carbyne complexes 1-3 react with (C(2)H(5))(2)NH, (iC(3)H(7))(2)NH, and (C(6)H(11))(2)NH under the same conditions with ring cleavage of the COT ligand to produce the novel diiron-bridging carbene inner salts [Fe(2)[mu-C(Ar)C(8)H(8)NR(2)](CO)(4)] (7, Ar=C(6)H(5), R=C(2)H(5); 8, Ar=p-CH(3)C(6)H(4), R=C(2)H(5); 9, Ar=p-CF(3)C(6)H(4), R=C(2)H(5); 10, Ar=C(6)H(5), R=iC(3)H(7); 11, Ar=p-CH(3)C(6)H(4), R=iC(3)H(7); 12, Ar=p-CF(3)C(6)H(4), R=iC(3)H(7); 13, Ar=C(6)H(5), R=C(6)H(11); 14, Ar=p-CH(3)C(6)H(4), R=C(6)H(11), 15, Ar=p-CF(3)C(6)H(4), R=C(6)H(11)). Piperidine reacts similarly with cationic carbyne complex 3 to afford the corresponding bridging carbene inner salt [Fe(2)[mu-C(Ar)C(8)H(8)N(CH(2))(5)](CO)(4)] (16). Compound 9 was transformed into a new diiron-bridging carbene inner salt 17, the trans isomer of 9, by heating in benzene. Unexpectedly, the reaction of C(6)H(5)NH(2) with 2 gave a novel COT iron-carbene complex [Fe(2)[=C(C(6)H(4)CH(3)-p)NHC(6)H(5)](mu-CO)(CO)(3)(eta(8)-C(8)H(8))] (18). However, the analogous reactions of 2-naphthylamine with 2 and of p-CF(3)C(6)H(4)NH(2) with 3 produce novel chelated iron-carbene complexes [Fe(2)[=C(C(6)H(4)CH(3)-p)NC(10)H(7)](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (19) and [Fe(2)[=C(C(6)H(4)CF(3)-p)NC(6)H(4)CF(3)-p](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (20), respectively. Compound 18 can also be transformed into the analogous chelated iron-carbene complex [Fe(2)[=C(C(6)H(4)CH(3)-p)NC(6)H(5)](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (21). The structures of complexes 6, 9, 15, 17, 18, and 21 have been established by X-ray diffraction studies.     

Ligand rotation in [Ar(R)N]3M-N2-M'[N(R)Ar]3(M, M' = MoIII, NbIII; R = iPr and tBu) dimers

Earlier calculations on the model N2-bridged dimer (micro-N2)-{Mo[NH2]3}2 revealed that ligand rotation away from a trigonal arrangement around the metal centres was energetically favourable resulting in a reversal of the singlet and triplet energies such that the singlet state was stabilized 13 kJ mol(-1) below the D(3d) triplet structure. These calculations, however, ignored the steric bulk of the amide ligands N(R)Ar (R =iPr and tBu, Ar = 3,5-C6H3Me2) which may prevent or limit the extent of ligand rotation. In order to investigate the consequences of steric crowding, density functional calculations using QM/MM techniques have been performed on the Mo(III)Mo(III) and Mo(III)Nb(III) intermediate dimer complexes (mu-N(2))-{Mo[N(R)Ar]3}2 and [Ar(R)N]3Mo-(mu-N2)-Nb[N(R)Ar]3 formed when three-coordinate Mo[N(R)Ar]3 and Nb[N(R)Ar]3 react with dinitrogen. The calculations indicate that ligand rotation away from a trigonal arrangement is energetically favourable for all of the ligands investigated and that the distortion is largely electronic in origin. However, the steric constraints of the bulky amide groups do play a role in determining the final orientation of the ligands, in particular, whether the ligands are rotated at one or both metal centres of the dimer. Analogous to the model system, QM/MM calculations predict a singlet ground state for the (mu-N2)-{Mo[N(R)Ar]3}2 dimers, a result which is seemingly at odds with the experimental triplet ground state found for the related (mu-N2)-{Mo[N(tBu)Ph]3}2 system. However, QM/MM calculations on the (mu-N2)-{Mo[N(tBu)Ph]3}2 dimer reveal that the singlet-triplet gap is nearly 20 kJ mol(-1) smaller and therefore this complex is expected to exhibit very different magnetic behaviour to the (mu-N2)-{Mo[N(R)Ar]3}2 system.     

beta-Diiminato ligand (L) transformations in reactions of KL with PI3 and I2 [L = {N(C6H3Pr(i)2-2,6)C(H)}2CPh

The reaction of the potassium beta-diiminate KL (L = [{N(Ar)C(H)}(2)CPh](-); Ar = C(6)H(3)Pr(i)(2)-2,6) with PI(3) unexpectedly produced a phosphenium salt of the intermolecularly C,C-coupled ligand [P(I){N(Ar)CH}(2)C(C(6)H(4)-4)C(Ph)(CH[double bond, length as m-dash]NAr)(2)](+)[I(3)](-), while an intramolecularly N,N-coupled salt [N[upper bond 1 start](Ar)C(H)C(Ph)C(H)N[upper bond 1 end](Ar)](+)[I(5)](-) was isolated from KL + I(2).     

On the origin of selective nitrous oxide N-N bond cleavage by three-coordinate molybdenum(III) complexes

Reaction of Mo(N[R]Ar)(3) (R = (t)Bu or C(CD(3))(2)CH(3)) with N(2)O gives rise exclusively to a 1:1 mixture of nitride NMo(N[R]Ar)(3) and nitrosyl ONMo(N[R]Ar)(3), rather than the known oxo complex OMo(N[R]Ar)(3) and dinitrogen. Solution calorimetry measurements were used to determine the heat of reaction of Mo(N[R]Ar)(3) with N(2)O and, independently, the heat of reaction of Mo(N[R]Ar)(3) with NO. Derived from the latter measurements is an estimate (155.3 +/- 3.3 kcal.mol(-1)) of the molybdenum-nitrogen bond dissociation enthalpy for the terminal nitrido complex, NMo(N[R]Ar)(3). Comparison of the new calorimetry data with those obtained previously for oxo transfer to Mo(N[R]Ar)(3) shows that the nitrous oxide N-N bond cleavage reaction is under kinetic control. Stopped-flow kinetic measurements revealed the reaction to be first order in both Mo(N[R]Ar)(3) and N(2)O, consistent with a mechanism featuring post-rate-determining dinuclear N-N bond scission, but also consistent with cleavage of the N-N bond at a single metal center in a mechanism requiring the intermediacy of nitric oxide. The new 2-adamantyl-substituted molybdenum complex Mo(N[2-Ad]Ar)(3) was synthesized and found also to split N(2)O, resulting in a 1:1 mixture of nitrosyl and nitride products; the reaction exhibited first-order kinetics and was found to be ca. 6 times slower than that for the tert-butyl-substituted derivative. Discussed in conjunction with studies of the 2-adamantyl derivative Mo(N[2-Ad]Ar)(3) is the role of ligand-imposed steric constraints on small-molecule, e.g. N(2) and N(2)O, activation reactivity. Bradley's chromium complex Cr(N(i)Pr(2))(3) was found to be competitive with Mo(N[R]Ar)(3) for NO binding, while on its own exhibiting no reaction with N(2)O. Competition experiments permitted determination of ratios of second-order rate constants for NO binding by the two molybdenum complexes and the chromium complex. Analysis of the product mixtures resulting from carrying out the N(2)O cleavage reactions with Cr(N(i)Pr(2))(3) present as an in situ NO scavenger rules out as dominant any mechanism involving the intermediacy of NO. Simplest and consistent with all the available data is a post-rate-determining bimetallic N-N scission process. Kinetic funneling of the reaction as indicated is taken to be governed by the properties of nitrous oxide as a ligand, coupled with the azophilic nature of three-coordinate molybdenum(III) complexes.     

1‐Azaallyl Complexes of NiII,PdII, and TiIII

The metal complexes [Ni{N(Ar)C(R)C(H)Ph}₂) ( 2 ) (Ar = 2,6‐Me₂C₆H₃, R = SiMe₃), [Ti(Cp₂){N(R)C(Bu^t)C(H)R}] ( 3 ), M{N(R)C(Bu^t)C(H)R}I [M = Ni ( 4 a ) or Pd ( 4 b )] and [M{N(R)C(Bu^t)C(H)R}I(PPh₃)] [M = Ni ( 5 a ) or Pd ( 5 b )] have been prepared from a suitable metal halide and lithium precursor of ( 2 ) or ( 3 ) or, alternatively from [M(LL)₂] (M = Ni, LL = cod; M = Pd, LL = dba) and the ketimine RN = C(Bu^t)CH(I)R ( 1 ). All compounds, except 4 were fully characterised, including the provision of X‐ray crystallographic data for complex 5 a .     

Mixed-ligand uranyl(V) beta-diketiminate/beta-diketonate complexes: synthesis and characterization

The reaction of [UO 2(Ar 2nacnac)Cl] 2 [Ar 2nacnac = (2,6- (i)Pr 2C 6H 3)NC(Me)CHC(Me)N(2,6- (i)Pr 2C 6H 3)] with Na(RC(O)CHC(O)R) (R = Me, Ph, CF 3) in tetrahydrofuran results in the formation of UO 2(Ar 2nacnac)(RC(O)CHC(O)R) (R = Me, 1; Ph, 2; CF 3, 3), which can be isolated in moderate yields. The structures of 1 and 2 have been confirmed by X-ray crystallography, while the solution redox properties of 1- 3 have been measured by cyclic voltammetry. Complexes 1- 3 exhibit reduction features at -1.82, -1.59, and -1.39 V (vs Fc/Fc (+)), respectively, at a scan rate of 100 mV.s (-1). The decrease in the reduction potential follows the electron-withdrawing ability of each beta-diketonate ligand. Chemical reduction of 1 and 2 with Cp* 2Co in toluene yields [Cp* 2Co][UO 2(Ar 2nacnac)(RC(O)CHC(O)R)] (R = Me, 4; Ph, 5), while reduction of 3 with Cp 2Co provides [Cp 2Co][UO 2(Ar 2nacnac)(CF 3C(O)CHC(O)CF 3)] ( 6). Complexes 4- 6 have been fully characterized, while the solid-state molecular structure of 5 has also been determined. In contrast to the clean reduction that occurs with Cp* 2Co, reduction of 1 with sodium ribbon, followed by cation exchange with [NEt 4]Cl, produces [NEt 4][UO 2(Ar 2nacnac)(H 2CC(O)CH(O)CMe)] ( 7) in modest yield. This product results from the formal loss of H (*) from a methyl group of the acetylacetonate ligand. Alternately, complex 7 can be synthesized by deprotonation of 1 with NaNTMS 2 in good yield.