Al and Zn complexes bearing N,N,N-tridentate quinolinyl anilido-imine ligands: synthesis, characterization and catalysis in l-lactide polymerization

Reactions of N,N,N-tridentate quinolinyl anilido-imine ligands with AlMe(3) afford mononuclear aluminum complexes {κ(3)-[{2-[ArN[double bond, length as m-dash]C(H)]C(6)H(4)}N(8-C(9)H(6)N)]}AlMe(2) (Ar = 2,6-Me(2)C(6)H(3) (1a), 2,6-Et(2)C(6)H(3) (1b), 2,6-(i)Pr(2)C(6)H(3) (1c)) or dinuclear complexes AlMe(3){κ(1)-[{2-[ArN[double bond, length as m-dash]C(H)C(6)H(4)]N(8-C(9)H(6)N)}-κ(2)]AlMe(2) (R = 2,6-Me(2)C(6)H(3) (2a), 2,6-Et(2)C(6)H(3) (2b), 2,6-(i)Pr(2)C(6)H(3) (2c)) depending on the ratios of reactants used. Similar reactions of ZnEt(2) with these ligands give the monoligated ethyl zinc complexes {κ(3)-[{2-[ArN[double bond, length as m-dash]C(H)]C(6)H(4)}N(8-C(9)H(6)N)]}ZnEt (Ar = 2,6-Me(2)C(6)H(3) (3a), 2,6-Et(2)C(6)H(3) (3b), 2,6-(i)Pr(2)C(6)H(3) (3c)) or bisligated complexes {κ(3)-[{2-[ArN[double bond, length as m-dash]C(H)]C(6)H(4)}N(8-C(9)H(6)N)]}Zn{κ(2)-[{2-[ArN[double bond, length as m-dash]C(H)]C(6)H(4)}N(8-C(9)H(6)N)]} (Ar = 2,6-Me(2)C(6)H(3) (4a), 2,6-Et(2)C(6)H(3) (4b), 2,6-(i)Pr(2)C(6)H(3) (4c)). These complexes were well characterized by NMR and the structures of 1a, 2a, 2c, 3b and 4c were confirmed by X-ray diffraction analysis. The aluminum and zinc complexes were tested to initiate lactide polymerization in which the zinc complexes show moderate to high activities in the presence of benzyl alcohol.     

Synthesis and characterisation of zinc gallyl complexes: first structural elucidations of Zn-Ga bonds

Reactions of the anionic gallium(i) heterocycle, [:Ga{[N(Ar)C(H)](2)}](-) (Ar = C(6)H(3)Pr(i)(2)-2,6), with two N,N-chelated zinc chloride complexes have yielded the compounds, [{Pr(i)(2)NC[N(Ar)](2)}ZnGa{[N(Ar)C(H)](2)}] and [(tmeda)Zn{Ga{[N(Ar)C(H)](2)}}(2)] which contain the first crystallographically characterised Zn-Ga bonds.     

Multiple pathways for dinitrogen activation during the reduction of an Fe Bis(iminepyridine) complex

Reduction of the bis(iminopyridine) FeCl(2) complex {2,6-[2,6-(iPr)(2)PhN=C(CH(3))](2)(C(5)H(3)N)}FeCl(2) using NaH has led to the formation of a surprising variety of structures depending on the amount of reductant. Some of the species reported in this work were isolated from the same reaction mixture, and their structures suggest the presence of multiple pathways for dinitrogen activation. The reaction with 3 equiv of NaH afforded {2-[2,6-(iPr)(2)PhN=C(CH(3))]-6-[2,6-(iPr)(20PhN-C=CH(2)](C(5)H(3)N)}Fe(micro,eta(2)-N(2))Na (THF) (1) containing one N(2) unit terminally bound to Fe and side-on attached to the Na atom. In the process, one of the two imine methyl groups has been deprotonated, transforming the neutral ligand into the corresponding monoanionic version. When 4 equiv were employed, two other dinitrogen complexes {2-[2,6-(iPr)(2)PhN=C(CH(3))]-6-[2,6-(iPr)(2)PhN-C=CH(2)](C(5)H(3)N)}Fe(micro-N2)Na(Et(2)O)(3) (2) and {2,6-[2,6-(iPr)(2)PhN=C(CH(3))](2)(C(5)H(3)N)}Fe(micro-N(2))Na[Na(THF)(2)] (3) were obtained from the same reaction mixture. Complex 2 is chemically equivalent to 1, the different degree of solvation of the alkali cation being the factor apparently responsible for the sigma-bonding mode of ligation of the N(2) unit to Na, versus the pi-bonding mode featured in 1. In complex 3, the ligand remains neutral but a larger extent of reduction has been obtained, as indicated by the presence of two Na atoms in the structure. A further increase in the amount of reductant (12 equiv) afforded a mixture of {2-[2,6-(iPr)(2)PhN=C(CH(3))]-6-[2,6-(iPr)(2)PhN-C=CH(2)](C(5)H(3)N)}Fe-N(2) (4) and [{2,6-[2,6-(iPr)(2)PhN=C(CH(3))](2)(C(5)H(3)N)}Fe-N(2)](2)(micro-Na) [Na(THF)(2)](2) (5) which were isolated by fractional crystallization. Complex 4, also containing a terminally bonded N(2) unit and a deprotonated anionic ligand bearing no Na cations, appears to be the precursor of 1. The apparent contradiction that excess NaH is required for its successful isolation (4 is the least reduced complex of this series) is most likely explained by the formation of the partner product 5, which may tentatively be regarded as the result of aggregation between 1 and 3 (with the ligand system in its neutral form). Finally, reduction carried out in the presence of additional free ligand afforded {2,6-[2,6-(iPr)(2)PhN=C(CH(3))](2)(C(5)H(3)N)}Fe(eta(1)-N(2)){2,6-[2,6-(iPr)(2)PhN=C(CH(3))](20(NC(5)H(2))}[Na(THF)(2)] (6) and {2,6-[2,6-(iPr)(2)PhN=C(CH(3))](2)(C(5)H(3)N)}Fe{2,6-[2,6-(iPr)(2)PhN=C(CH(3))](2)(NC(5)H(2))}Na(THF)(2)) (7). In both species, the Fe metal is bonded to the pyridine ring para position of an additional (L)Na unit. Complex 6 chemically differs from 7 (the major component) only for the presence of an end-on coordinated N(2).     

Rare earth metal bis(amide) complexes bearing amidinate ancillary ligands: synthesis, characterization, and performance as catalyst precursors for cis-1,4 selective polymerization of isoprene

A family of rare earth metal bis(amide) complexes bearing monoanionic amidinate [RC(N-2,6-Me(2)C(6)H(3))(2)](-) (R = cyclohexyl (Cy), phenyl (Ph)) as ancillary ligands were synthesized and characterized. One-pot salt metathesis reaction of anhydrous LnCl(3) with one equivalent of amidinate lithium [RC(N-2,6-Me(2)C(6)H(3))(2)]Li, following the introduction of two equivalents of NaN(SiMe(3))(2) in THF at room temperature afforded the neutral and unsolvated mono(amidinate) rare earth metal bis(amide) complexes [RC(N-2,6-Me(2)C(6)H(3))(2)]Y[N(SiMe(3))(2)](2) (R = Cy (1); R = Ph (2)), and the "ate" mono(amidinate) rare earth metal bis(amide) complex [CyC(N-2,6-Me(2)C(6)H(3))(2)]Lu[N(SiMe(3))(2)](2)(μ-Cl)Li(THF)(3) (3) in 61-72% isolated yields. These complexes were characterized by elemental analysis, NMR spectroscopy, FT-IR spectroscopy, and X-ray single crystal diffraction. Single crystal structural determination revealed that the central metal in complexes 1 and 2 adopts a distorted tetrahedral geometry, and in complex 3 forms a distorted trigonal bipyramidal geometry. In the presence of AlMe(3), and in combination with one equimolar amount of [Ph(3)C][B(C(6)F(5))(4)], complexes 1 and 2 showed high activity towards isoprene polymerization to give high molecular weight polyisoprene (M(n) > 10(4)) with good cis-1,4 selectivity (>90%).     

Monomeric, one- and two-dimensional networks incorporating (2,6-Me2C6H3S)2Pb building blocks

The amine coordination of lead(II) has been examined through the preparation and structural analysis of Lewis base adducts of bis(thiolato)lead(II) complexes. Reaction of Pb(OAc)(2) with 2,6-dimethylbenzenethiol affords (2,6-Me(2)C(6)H(3)S)(2)Pb (6) in high yield. The solubility of 6 in organic solvents allows for the preparation of the 1:2 Lewis acid-base adduct [(2,6-Me(2)C(6)H(3)S)(2)Pb(py)(2)](7), and 1:1 adducts [(2,6-Me(2)C(6)H(3)S)(2)Pb(micro(2)-bipy)](infinity](8) and [(2,6-Me(2)C(6)H(3)S)(2)Pb(micro(2)-pyr)](infinity)(9)(where py = pyridine, bipy = 4,4'-bipyridyl and pyr = pyrazine) from reaction with an excess of the appropriate amine. In contrast to 7, reaction of (C(6)H(5)S)(2)Pb (1) with pyridine afforded the 2:1 adduct [(C(6)H(5)S)(4)Pb(2)(py)](infinity)(10). Compounds were characterized via elemental analysis, FT-IR, solution (1)H and (13)C[(1)H](6) NMR spectroscopy, and X-ray crystallography (7-10). The structures of 7-9 show the thiolate groups occupying two equatorial positions and two amine nitrogen atoms occupying axial coordination sites, yielding distorted see-saw coordination geometries, or distorted trigonal bipyramids if an equatorial lone pair on lead is considered. The absence of intermolecular contacts in 7 and 8 result in monomeric and one-dimensional polymeric structures, respectively. Weak Pb...S intermolecular contacts in 9 result in the formation of a two-dimensional macrostructure. In contrast, the structure of , shows extensive intermolecular Pb...S interactions, resulting in five- and six-coordinate bonding environments for lead(II), and a complex polymeric structure in the solid state. This demonstrates the ability of the 2,6-dimethylphenylthiolate ligand to limit intermolecular lead-sulfur interactions, while allowing the axial coordination of amine Lewis base ligands.     

New titanium complexes with symmetric or asymmetric cis-9,10-dihydrophenanthrenediamide ligands formed through sequential intramolecular C-C bond-forming reactions

A series of new titanium(IV) complexes with symmetric or asymmetric cis-9,10-dihydrophenanthrenediamide ligands, cis-9,10-PhenH(2)(NR)(2)Ti(O(i)Pr)(2) [PhenH(2) = 9,10-dihydrophenanthrene, R = 2,6-(i)Pr(2)C(6)H(3) (2a), 2,6-Et(2)C(6)H(3) (2b), 2,6-Me(2)C(6)H(3) (2c)], cis-9,10-PhenH(2)(NR(1))(NR(2))Ti(O(i)Pr)(2) [R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Et(2)C(6)H(3) (2d); R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Me(2)C(6)H(3) (2e)], and [cis-9,10-PhenH(2)(NR(1))(2)][o-C(6)H(4)(CH=NR(2))]TiO(i)Pr [R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Et(2)C(6)H(3) (3a); R(1) = 2,6-(i)Pr(2)C(6)H(3), 2,6-Me(2)C(6)H(3) (3b)], have been synthesized from the reactions of TiCl(2)(O(i)Pr)(2) with o-C(6)H(4)(CH=NR)Li [R = 2,6-(i)Pr(2)C(6)H(3), 2,6-Et(2)C(6)H(3), 2,6-Me(2)C(6)H(3)]. The symmetric complexes 2a-2c were obtained from the reactions of TiCl(2)(O(i)Pr)(2) with 2 equiv of the corresponding o-C(6)H(4)(CH=NR)Li followed by intramolecular C-C bond-forming reductive elimination and oxidative coupling processes, while the asymmetric complexes 2d-2e were formed from the reaction of TiCl(2)(O(i)Pr)(2) with two different types of o-C(6)H(4)(CH=NR)Li sequentially. The complexes 3a and 3b were also isolated from the reactions for complexes 2d and 2e. All complexes were characterized by (1)H and (13)C NMR spectroscopy, and the molecular structures of 2a, 2b, 2e, and 3a were determined by X-ray crystallography.     

Synthesis and structures of a 3-sila-beta-diketiminatomagnesium bromide, ketenimide and triflate

The crystalline compounds [Mg(Br)(L)(thf)].0.5Et2O [L = {N(R)C(C6H3Me2-2,6)}2SiR, R = SiMe3] (1), [Mg(L){N=C=C(C(Me)=CH)2CH2}(D)2] [D = NCC6H3Me2-2,6 (2), thf (3)] and [{Mg(L)}2{mu-OSO(CF3)O-[mu}2] (4) were prepared from (a) Si(Br)(R){C(C6H3Me2-2,6)=NR}2 and Mg for (1), (b) [Mg(SiR3)2(thf)2] and 2,6-Me2C6H3CN (5 mol for (2), 3 mol for (3)), and (c) (2) + Me3SiOS(O)2CF3 for (4); a coproduct from (c) is believed to have been the trimethylsilyl ketenimide Me3SiN=C=C{C(Me)=CH}2CH2 (5).     

Synthesis and Characterization of Sterically Encumbered Derivatives of Aluminum Hydrides and Halides: Assessment of Steric Properties of Bulky Terphenyl Ligands

The synthesis and characterization of several sterically encumbered monoterphenyl derivatives of aluminum halides and aluminum hydrides are described. These compounds are [2,6-Mes(2)C(6)H(3)AlH(3)LiOEt(2)](n)() (1), (Mes = 2,4,6-Me(3)C(6)H(2)-), 2,6-Mes(2)C(6)H(3)AlH(2)OEt(2) (2), [2,6-Mes(2)C(6)H(3)AlH(2)](2) (3), 2,6-Mes(2)C(6)H(3)AlCl(2)OEt(2) (4), [2,6-Mes(2)C(6)H(3)AlCl(3)LiOEt(2)](n)() (5), [2,6-Mes(2)C(6)H(3)AlCl(2)](2) (6), TriphAlBr(2)OEt(2) (7), (Triph = 2,4,6-Ph(3)C(6)H(2)-), [2,6-Trip(2)C(6)H(3)AlH(3)LiOEt(2)](2) (8) (Trip = 2,4,6-i-Pr(3)C(6)H(2)-), 2,6-Trip(2)C(6)H(3)AlH(2)OEt(2) (9), [2,6-Trip(2)C(6)H(3)AlH(2)](2) (10), 2,6-Trip(2)C(6)H(3)AlCl(2)OEt(2) (11), and the partially hydrolyzed derivative [2,6-Trip(2)C(6)H(3)Al(Cl)(0.68)(H)(0.32)(&mgr;-OH)](2).2C(6)H(6) (12). The structures of 2, 3a, 4, 6, 7, 9a, 10a, 10b, 11, and 12 were determined by X-ray crystallography. The structures of 3a, 9a, 10a, and 10b, are related to 3, 9, and 10, respectively, by partial occupation of chloride or hydride by hydroxide. The compounds were also characterized by (1)H, (13)C, (7)Li, and (27)Al NMR and IR spectroscopy. The major conclusions from the experimental data are that a single ortho terphenyl substituent of the kind reported here are not as effective as the ligand Mes (Mes = 2,4,6-t-Bu(3)C(6)H(2)-) in preventing further coordination and/or aggregation involving the aluminum centers. In effect, one terphenyl ligand is not as successful as a Mes substituent in masking the metal through agostic and/or steric effects.     

Synthesis and structural characterization of alkaline-earth-metal bis(amido)silane and lithium oxobis(aminolato)silane complexes

Several of alkaline-earth-metal complexes [(η(2):η(2):μ(N):μ(N)-Li)(+)](2)[{η(2)-Me(2)Si(DippN)(2)}(2)Mg](2-) (4), [η(2)(N,N)-Me(2)Si(DippN)(2)Ca·3THF] (5), [η(2)(N,N)-Me(2)Si(DippN)(2)Sr·THF] (6), and [η(2)(N,N)-Me(2)Si(DippN)(2)Ba·4THF] (7) of a bulky bis(amido)silane ligand were readily prepared by the metathesis reaction of alkali-metal bis(amido)silane [Me(2)Si(DippNLi)(2)] (Dipp = 2,6-i-Pr(2)C(6)H(3)) and alkaline-earth-metal halides MX(2) (M = Mg, X = Br; M = Ca, Sr, Ba, X = I). Alternatively, compounds 5-7 were synthesized either by transamination of M[N(SiMe(3))(2)](2)·2THF (M = Ca, Sr, Ba) and [Me(2)Si(DippNH)(2)] or by transmetalation of Sn[N(SiMe(3))(2)](2), [Me(2)Si(DippNH)(2)], and metallic calcium, strontium, and barium in situ. The metathesis reaction of dilithium bis(amido)silane [Me(2)Si(DippNLi)(2)] and magnesium bromide in the presence of oxygen afforded, however, an unusual lithium oxo polyhedral complex {[(DippN(Me(2)Si)(2))(μ-O)(Me(2)Si)](2)(μ-Br)(2)[(μ(3)-Li)·THF](4)(μ(4)-O)(4)(μ(3)-Li)(2)} (8) with a square-basket-shaped core Li(6)Br(2)O(4) bearing a bis(aminolato)silane ligand. All complexes were characterized using (1)H, (13)C, and (7)Li NMR and IR spectroscopy, in addition to X-ray crystallography.     

Transfer hydrogenation processes to mu(3)-alkylidyne groups on the organotitanium oxide [Ti(3)Cp*O(3)

The photochemical treatment of mu(3)-alkylidyne complexes [[TiCp*(mu-O)](3)(mu(3)-CR)] (R=H (1), Me (2), Cp*=eta(5)-C(5)Me(5)) with the amines (2,6-Me(2)C(6)H(3))NH(2), Et(2)NH, and Ph(2)NH and the imine Ph(2)C=NH leads to the partial hydrogenation of the alkylidyne moiety that is supported on the organometallic oxide, [Ti(3)Cp*O(3)], and the formation of new oxoderivatives [[TiCp*(3)(mu-CHR)(R'NR")] (R"=2,6-Me(2)C(6)H(3), R'=H, R=H (3), Me (4); R'=R"=Et, R=H (5), Me (6); R'=R"=Ph, R=H (7), Me (8)) and [[TiCp*(mu-O)](3)(mu-CHR)(N=CPh(2))] (R=H (9), R=Me (10)), respectively. A sequential transfer hydrogenation process occurs when complex 1 is treated with tBuNH(2), which initially gives the mu-methylene [[TiCp*(mu-O)](3)(mu-CH(2))(HNtBu)] (11) complex and finally, the alkyl derivative [[TiCp*(mu-O)](3)(mu-NtBu)Me] (12). Furthermore, irradiation of solutions of the mu(3)-alkylidyne complexes 1 or 2 in the presence of diamines o-C(6)H(4)(NH(2))(2) and H(2)NCH(2)CH(2)NH(2) (en) affords [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(6)H(4)NH)] (13) and [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(2)H(4)NH)] (14) by either methane or ethane elimination, respectively. In the reaction of 1 with en, an intermediate complex [[TiCp*(mu-O)](3)(mu-CH(2))(NHCH(2)CH(2)NH(2))] (15) is detected by (1)H NMR spectroscopy. Thermal treatment of the complexes 4-10 quantitatively regenerates the starting mu(3)-alkylidyne compounds and the amine R'(2)NH or the imine Ph(2)C=NH; however, heating of solutions of 3 or 4 in [D(6)]benzene or a equimolecular mixture of both at 170 degrees C produces methane, ethane, or both, and the complex [[TiCp*(mu-O)](3)[mu(3)-eta(2)-NC(6)H(3)(Me)CH(2)]] (16). The molecular structure of 8 has been established by single-crystal X-ray analysis.     

Dinitrogen activation, partial reduction, and formation of coordinated imide promoted by a chromium diiminepyridine complex

Reduction of {2,6-[2,6-(i-Pr)2PhN=C(CH3)]2(C5H3N)}CrCl (3) with NaH afforded the dinuclear dinitrogen complex {[{2,6-[2,6-(i-Pr)2PhN=C(CH3)]2(C5H3N)}Cr(THF)]2(mu-N2)}.THF (5). Reaction carried in exclusion of dinitrogen afforded instead deprotonation of the ligand with the formation of {2-[2,6-(i-Pr)2PhN=C(CH3)]-6-[2,6-(i-Pr)2PhNC=CH2](C5H3N)}Cr(THF) (4). Further reduction of 5 with NaH yielded a curious dinuclear compound formulated as [{2,6-[2,6-(i-Pr)2PhN=C(CH3)]2(C5H3N)}Cr(THF)][{2-[2,6-(i-Pr)2PhN=C(CH3)]-6-[2,6-(i-Pr)2PhNC=CH2](C5H3N)}Cr(THF)](mu-N2 H)(mu-Na)2 (6) containing two sodium atoms only bound to the dinitrogen unit and the pi systems of the two diiminepyridine ligands. Subsequent reduction with NaH triggered a complex series of events, leading to the formation of a species formulated as {2-[2,6-(i-Pr)2PhN=C(CH3)]-6-[2,6-(i-Pr)2PhNC=CH2](C5H3N)}Cr(mu-NH)][Na(THF)] (7) on the basis of crystallographic, spectroscopic, isotopic labeling, and chemical degradation experiments.     

Synthesis and characterization of three-coordinate and related beta-diketiminate derivatives of manganese,iron, and cobalt

Treatment of M[N(SiMe(3))(2)](2) (M = Mn, Fe, Co) with various bulky beta-diketimines afforded a variety of new three-coordinate complexes which were characterized by UV-vis, (1)H NMR and IR spectroscopy, magnetic measurements, and X-ray crystallography. Reaction of the beta-diketimine H(Dipp)NC(Me)CHC(Me)N(Dipp) (Dipp(2)N(wedge)NH; Dipp = C(6)H(3)-2,6-Pr(i)(2)) with M[N(SiMe(3))(2)](2) (M = Mn or Co) gave Dipp(2)N(wedge)NMN(SiMe(3))(2) (M = Mn, 1; Co, 3) while the reaction of Fe[N(SiMe(3))(2)](2) with Ar(2)N(wedge)NH (Ar = Dipp, C(6)F(5), Mes, C(6)H(3)-2,6-Me(2), or C(6)H(3)-2,6-Cl(2)) afforded the series of iron complexes Ar(2)N(wedge)NFe[N(SiMe(3))(2)] (Ar = Dipp, 2a; C(6)F(5), 2b; Mes, 2c; C(6)H(3)-2,6-Me(2), 2d; C(6)H(3)-2,6-Cl(2), 2e). This represents a new synthetic route to beta-diketiminate complexes of these metals. The four-coordinate bis-beta-diketiminate complex Fe[N(wedge)N(C(6)F(5))(2)](2), 4, was also isolated as a byproduct from the synthesis of 2b. Direct reaction of the Dipp(2)N(wedge)NLi with CoCl(2) gave the "ate" salt Dipp(2)N(wedge)NCoCl(2)Li(THF)(2), 5, in which the lithium chloride has formed a complex with Dipp(2)N(wedge)NCoCl through chloride bridging. The Fe(III) species Dipp(2)N(wedge)NFeCl(2), 6, was obtained cleanly from the reaction of FeCl(3) with Dipp(2)N(wedge)NLi. Magnetic measurements showed that all the complexes have a high spin configuration. The different substituents in the series of iron complexes 2a-e allowed assignment of their paramagnetically shifted (1)H NMR spectra. The X-ray crystal structures 1-2d and 3 showed that they have a distorted three-coordinate planar configuration at the metals whereas complexes 4-6 have highly distorted four-coordinate geometries.     

The reactivity of gallium-(I), -(II) and -(III) heterocycles towards Group 15 substrates: attempts to prepare gallium-terminal pnictinidene complexes

The reactivity of a series of Ga(I), Ga(II) and Ga(III) heterocyclic compounds towards a number of Group 15 substrates has been investigated with a view to prepare examples of gallium-terminal pnictinidene complexes. Although no examples of such complexes were isolated, a number of novel complexes have been prepared. The reactions of the gallium(I) N-heterocyclic carbene analogue, [K(tmeda)][:Ga{[N(Ar)C(H)](2)}] (Ar = 2,6-diisopropylphenyl) with cyclo-(PPh)(5) and PhN[double bond, length as m-dash]NPh led to the unusual anionic spirocyclic complexes, [{kappa(2)P,P'-(PhP)(4)}Ga{[N(Ar)C(H)](2)}](-) and [{kappa(2)N,C-PhNN(H)(C(6)H(4))}Ga{[N(Ar)C(H)](2)}](-), via formal reductions of the Group 15 substrate. The reaction of the digallane(4), [Ga{[N(Ar)C(H)](2)}](2), with (Me(3)Si)N(3) afforded the paramagnetic, dimeric imido-gallane complex, [{[N(Ar)C(H) ](2)}Ga{mu-N(SiMe(3))}](2), via a Ga-Ga bond insertion process. In addition, the new gallium(III) phosphide, [GaI{P(H)Mes*}{[N(Ar)C(H)](2) }], Mes* = C(6)H(2)Bu(t)(3)-2,4,6; was prepared and treated with diazabicycloundecane (DBU) to give [Ga(DBU){P(H)Mes*}{[N(Ar)C(H)](2)}], presumably via a gallium-terminal phosphinidene intermediate, [Ga{[double bond, length as m-dash]PMes*}{[N(Ar)C(H)](2) }]. The possible mechanisms of all reactions are discussed, all new complexes have been crystallographically characterised and all paramagnetic complexes have been studied by ENDOR and/or EPR spectroscopy.     

Synthesis and structures of monomeric magnesium, calcium, strontium, and barium amides involving the N,N-(2,4,6-trimethylphenyl)(trimethylsilyl)amido ligand

An extended family of aryl-substituted alkaline earth metal silylamides M{N(2,4,6-Me3C6H2)(SiMe3)}donor(n) was prepared using alkane elimination (Mg), salt elimination (Ca, Sr, Ba), and direct metalation (Sr, Ba). Three different donors, THF, TMEDA (TMEDA = N,N,N',N'-tetramethylethylenediamine), and PMDTA (PMDTA = N,N,N',N',N'-pentamethyldiethylenetriamine) were employed to study their influence on the coordination chemistry of the target compounds, producing monomeric species with the composition M{N(2,4,6-Me3C6H2)(SiMe3)}2(THF)2 (M = Mg, Ca, Sr, Ba), M{N(2,4,6-Me3C6H2)(SiMe3)}2TMEDA (M = Ca, Ba), and M{N(2,4,6-Me3C6H2)(SiMe3)}2PMDTA (M = Sr, Ba). For the heavier metal analogues, varying degrees of agostic interactions are completing the coordination sphere of the metals. Compounds were characterized using IR and NMR spectroscopy in addition to X-ray crystallography.     

Synthesis and characterization of aryl substituted bis(2-pyridyl)amines and their copper olefin complexes: investigation of remote steric control over olefin binding

The aryl-functionalized pyridylamine 2-(i)PrC(6)H(4)N(H)py (1) and bis(2-pyridyl)amines of the type ArN(py)(2) for Ar = Mes (2), 2,6-Et(2)C(6)H(3) (3), 2-(i)PrC(6)H(4) (4), 2,6-(i)Pr(2)C(6)H(3) (5), and 1-naph (6), have been prepared by the palladium-catalyzed cross-coupling of substituted anilines with 2-bromopyridine, and have been characterized by (1)H and (13)C NMR NMR, FTIR, MS, and TGA. Complexes of these new N-aryl bis(2-pyridyl)amines have been prepared for the acid salts [H{ArN(py)(2)}]BF(4) where Ar = Mes (7) and 2-(i)PrC(6)H(4) (8), and the dimeric bridged complexes [Cu{ArN(py)(2)}(μ-X)(Y)](2) where X/Y = Cl(-) and Ar = Ph (9), 2-(i)PrC(6)H(4) (10), and 1-naph (11), in addition to X = OH(-), Y = H(2)O and Ar = Mes (12). The olefin complexes [Cu(Ar-dpa)(styrene)]BF(4) for Ar = Ph (13), Mes (14), 2-(i)PrC(6)H(4) (15), and 1-naph (16), in addition to the norborylene complexes of Ar = Mes (17) and 2-(i)PrC(6)H(4) (18) have been prepared and characterized by (1)H and (13)C NMR, FTIR, and TGA. The crystal structures have been determined for compounds 1-17. Secondary amine 1 crystallizes in hydrogen-bonded head-to-tail dimers, while the N-aryl bis(2-pyridyl)amines 2-6 crystallize in a three-bladed propellar conformation, having nearly planar geometries about the amine nitrogen. The geometry about copper centers in the dimeric complexes 9-12 is distorted trigonal bypyramidal, with the axial positions occupied by one of the two pyridyl nitrogens and one of the bridging ligands (i.e., Cl or OH). The copper atoms in each of the olefin complexes 13-17 are coordinated to the two pyridine nitrogen atoms and the appropriate olefin; consistent with a pseudo three-coordinate Cu(I) cation. Distortion of pyridyl ring geometries about the copper centers, and concomitant bending of the aryl groups away from the CuN(amine) vectors were found to correlate with the steric bulk of the aryl group present in both dimeric and olefin complexes. Such distortion is also observed to a lesser extent in the acid salts as well. The (1)H and (13)C NMR spectra of [Cu(Ar-dpa)(olefin)]BF(4) exhibit an upfield shift in the olefin signal as compared to free olefin. A good correlation exists between the (1)H and (13)C NMR Δδ values and olefin dissociation temperatures, confirming that the shift of the olefin NMR resonances upon coordination is associated with the binding strength of the complex.     

Discrete, solvent-free alkaline-earth metal cations: metal···fluorine interactions and ROP catalytic activity

Efficient protocols for the syntheses of well-defined, solvent-free cations of the large alkaline-earth (Ae) metals (Ca, Sr, Ba) and their smaller Zn and Mg analogues have been designed. The reaction of 2,4-di-tert-butyl-6-(morpholinomethyl)phenol ({LO(1)}H), 2-{[bis(2-methoxyethyl)amino]methyl}-4,6-di-tert-butylphenol ({LO(2)}H), 2-[(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)methyl]-4,6-di-tert-butylphenol ({LO(3)}H), and 2-[(1,4,7,10-tetraoxa-13-azacyclo-pentadecan-13-yl)methyl]-1,1,1,3,3,3-hexafluoropropan-2-ol ({RO(3)}H) with [H(OEt(2))(2)](+)[H(2)N{B(C(6)F(5))(3)}(2)](-) readily afforded the doubly acidic pro-ligands [{LO(1)}HH](+)[X](-) (1), [{LO(2)}HH](+)[X](-) (2), [{LO(3)}HH](+)[X](-) (3), and [{RO(3)}HH](+)[X](-) (4) ([X](-) = [H(2)N{B(C(6)F(5))(3)}(2)](-)). The addition of 2 to Ca[N(SiMe(3))(2)](2)(THF)(2) and Sr[N(SiMe(3))(2)](2)(THF)(2) yielded [{LO(2)}Ca(THF)(0.5)](+)[X](-) (5) and [{LO(2)}Sr(THF)](+)[X](-) (6), respectively. Alternatively, 5 could also be prepared upon treatment of {LO(2)}CaN(SiMe(3))(2) (7) with [H(OEt(2))(2)](+)[X](-). Complexes [{LO(3)}M](+)[X](-) (M = Zn, 8; Mg, 9; Ca, 10; Sr, 11; Ba, 12) and [{RO(3)}M](+)[X](-) (M = Zn, 13; Mg, 14; Ca, 15; Sr, 16; Ba, 17) were synthesized in high yields (70-90%) by reaction of 3 or 4 with the neutral precursors M[N(SiMe(3))(2)](2)(THF)(x) (M = Zn, Mg, x = 0; M = Ca, Sr, Ba, x = 2). All compounds were fully characterized by spectroscopic methods, and the solid-sate structures of compounds 1, 3, 7, 8, 13, 14, {15}(4)·3CD(2)Cl(2), {16}(4)·3CD(2)Cl(2), and {{17}(4)·EtOH}·3CD(2)Cl(2) were determined by X-ray diffraction crystallography. Whereas the complexes are monomeric in the case of Zn and Mg, they form bimetallic cations in the case of Ca, Sr and Ba; there is no contact between the metal and the weakly coordinating anion. In all metal complexes, the multidentate ligand is κ(6)-coordinated to the metal. Strong intramolecular M···F secondary interactions between the metal and F atoms from the ancillary ligands are observed in the structures of {15}(4)·3CD(2)Cl(2), {16}(4)·3CD(2)Cl(2), and {{17}(4)·EtOH}·3CD(2)Cl(2). VT (19)F{(1)H} NMR provided no direct evidence that these interactions are maintained in solution; nevertheless, significant Ae···F energies of stabilization of 25-26 (Ca, Ba) and 40 kcal·mol(-1) (Sr) were calculated by NBO analysis on DFT-optimized structures. The identity and integrity of the cationic complexes are preserved in solution in the presence of an excess of alcohol (BnOH, (i)PrOH) or L-lactide (L-LA). Efficient binary catalytic systems for the immortal ring-opening polymerization of L-LA (up to 3,000 equiv) are produced upon addition of an excess (5-50 equiv) of external protic nucleophilic agents (BnOH, (i)PrOH) to 8-12 or 13-17. PLLAs with M(n) up to 35,000 g·mol(-1) were produced in a very controlled fashion (M(w)/M(n) ≈ 1.10-1.20) and without epimerization. In each series of catalysts, the following order of catalytic activity was established: Mg ? Zn < Ca < Sr ≈ Ba; also, Ae complexes supported by the aryloxide ligand are more active than their parents supported by the fluorinated alkoxide ancillary, possibly owing to the presence of Ae···F interactions in the latter case. The rate law -d[L-LA]/dt = k(p)·[L-LA](1.0)·[16](1.0)·[BnOH](1.0) was established by NMR kinetic investigations, with the corresponding activation parameters ΔH(++) = 14.8(5) kcal·mol(-1) and ΔS(++) = -7.6(2.0) cal·K(-1)·mol(-1). DFT calculations indicated that the observed order of catalytic activity matches an increase of the L-LA coordination energy onto the cationic metal centers with parallel decrease of the positive metal charge.     

Reduction of carbodiimides by samarium(II) bis(trimethylsilyl)amides-formation of oxalamidinates and amidinates through C-C coupling or C-H activation

The reaction of [Sm{N(SiMe3)2}2(THF)2] (THF=tetrahydrofuran) with carbodiimides RN=C=NR (R=Cy, C6H3-2,6-iPr2) led to the formation of dinuclear SmIII complexes via differing C-C coupling processes. For R=Cy, the product [{(Me3Si)2N}2Sm(micro-C2N4Cy4)Sm{N(SiMe3)2}2] (1) has an oxalamidinate [C2N4Cy4]2- ligand resulting from coupling at the central C atoms of two CyNCNCy moieties. In contrast, for R=C6H3-2,6-iPr2, H transfer and an unusual coupling of two iPr methine C atoms resulted in a linked formamidinate complex, [{(Me3Si)2N}2Sm{micro-(RNC(H)N(Ar-Ar)NC(H)NR)}Sm{N(SiMe3)2}2] (2) (Ar-Ar=C6H3-2-iPr-6-C(CH3)2C(CH3)2-6'-C6H3-2'-iPr). Analogous reactions of RN=C=NR (R=Cy, C6H3-2,6-iPr2) with the SmII "ate" complex [Sm{N(SiMe2)3Na] gave 1 for R=Cy, but a novel C-substituted amidinate complex, [(THF)Na{N(R)C(NR)CH2Si(Me2)N(SiMe3)}Sm{N(SiMe3)2}2] (3), for R=C6H3-2,6-iPr2, via gamma C-H activation of a N(SiMe3)2 ligand.     

The synthesis, structure and ethene polymerisation catalysis of mono(salicylaldiminato) titanium and zirconium complexes

The silyl ethers 3-But-2-(OSiMe3)C6H3CH=NR (2a-e) have been prepared by deprotonation of the known iminophenols (1a-e) and treatment with SiClMe3 (a, R = C6H5; b, R = 2,6-Pri2C6H3; c, R = 2,4,6-Me3C6H2; d, R = 2-C6H5C6H4; e, R = C6F5). 2a-c react with TiCl4 in hydrocarbon solvents to give the binuclear complexes [Ti{3-But-2-(O)C6H3CH=N(R)}Cl(mu-Cl3)TiCl3] (3a-c). The pentafluorophenyl species 2e reacts with TiCl4 to give the known complex Ti{3-But-2-(O)C6H3CH=N(R)}2Cl2. The mononuclear five-coordinate complex, Ti{3-But-2-(O)C6H3CH=N(2,4,6-Me3C6H2)}Cl3 (4c), was isolated after repeated recrystallisation of 3c. Performing the dehalosilylation reaction in the presence of tetrahydrofuran yields the octahedral, mononuclear complexes Ti{3-But-2-(O)C6H3CH=N(R)}Cl3(THF) (5a-e). The reaction with ZrCl4(THF)2 proceeds similarly to give complexes Zr{3-But-2-(O)C6H3CH=N(R)}Cl3(THF) (6b-e). The crystal structures of 3b, 4c, 5a, 5c, 5e, 6b, 6d, 6e and the salicylaldehyde titanium complex Ti{3-But-2-(O)C6H3CH=O}Cl3(THF) (7) have been determined. Activation of complexes 5a-e and 6b-e with MAO in an ethene saturated toluene solution gives polyethylene with at best high activity depending on the imine substituent.     

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.     

Lithium aluminates on a molecular titanium oxide

Lithium aluminates Li[Al(O-2,6-Me(2)C(6)H(3))R'(3)] (R' = Et, Ph) react with the μ(3)-alkylidyne oxoderivative ligands [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-CR)] [R = H (1), Me (2)] to afford the aluminum-lithium-titanium cubane complexes [{R'(3)Al(μ-O-2,6-Me(2)C(6)H(3))Li}(μ(3)-O)(3){Ti(η(5)-C(5)Me(5))}(3)(μ(3)-CR)] [R = H, R' = Et (5), Ph (7); R = Me, R' = Et (6), Ph (8)]. Complex 7 evolves with the formation of a lithium dicubane species and a Li{Al(μ-O-2,6-Me(2)C(6)H(3))Ph(3)}(2)] unit.