Synthesis and Characterization of Ge(II), Sn(II), and Pb(II) Monoamides with -NH2 Ligands

The synthesis and characterization of the first divalent germanium, tin, and lead monoamide derivatives of the parent amide group -NH(2) are presented. They have the general formula (ArMNH(2))(2) (M = Ge, Ar = Ar'(C(6)H(3)-2,6-Pr(i)(2)) or Ar* (C(6)H(3)-2,6(C(6)H(2)-2,4,6-Pr(i)(3))); M = Sn, Ar = Ar*; M = Pb, Ar = Ar*). For germanium and tin, they were obtained by reacting the corresponding terphenyl halides of the group 14 elements with liquid ammonia in diethyl ether. The lead amide derivative (Ar*PbNH(2))(2) was synthesized by reaction of LiNH(2) with Ar*PbBr in diethyl ether. The compounds were characterized by IR and multinuclear NMR spectroscopies and by X-ray crystallography in the case of the (Ar'GeNH(2))(2) or (Ar*SnNH(2))(2) derivatives. They possess dimeric structures with two -NH(2) groups bridging the germanium and tin centers. For lead, the reaction with ammonia led to isolation of a stable ammine complex of formula Ar*PbBr(NH(3)) which was characterized by IR and NMR spectroscopies and by X-ray crystallography. It is the first structural characterization of a divalent lead ammine complex.     

Isomeric forms of heavier main group hydrides: experimental and theoretical studies of the [Sn(Ar)H]2 (Ar = terphenyl) system

A series of symmetric divalent Sn(II) hydrides of the general form [(4-X-Ar')Sn(mu-H)]2 (4-X-Ar' = C6H2-4-X-2,6-(C6H3-2,6-iPr2)2; X = H, MeO, tBu, and SiMe3; 2, 6, 10, and 14), along with the more hindered asymmetric tin hydride (3,5-iPr2-Ar*)SnSn(H)2(3,5-iPr2-Ar*) (16) (3,5-iPr2-Ar* = 3,5-iPr2-C6H-2,6-(C6H2-2,4,6-iPr3)2), have been isolated and characterized. They were prepared either by direct reduction of the corresponding aryltin(II) chloride precursors, ArSnCl, with LiBH4 or iBu2AlH (DIBAL), or via a transmetallation reaction between an aryltin(II) amide, ArSnNMe2, and BH3.THF. Compounds 2, 6, 10, and 14 were obtained as orange solids and have centrosymmetric dimeric structures in the solid state with long Sn...Sn separations of 3.05 to 3.13 A. The more hindered tin(II) hydride 16 crystallized as a deep-blue solid with an unusual, formally mixed-valent structure wherein a long Sn-Sn bond is present [Sn-Sn = 2.9157(10) A] and two hydrogen atoms are bound to one of the tin atoms. The Sn-H hydrogen atoms in 16 could not be located by X-ray crystallography, but complementary M?ssbauer studies established the presence of divalent and tetravalent tin centers in 16. Spectroscopic studies (IR, UV-vis, and NMR) show that, in solution, compounds 2, 6, 10, and 14 are predominantly dimeric with Sn-H-Sn bridges. In contrast, the more hindered hydrides 16 and previously reported (Ar*SnH)2 (17) (Ar* = C6H3-2,6-(C6H2-2,4,6-iPr3)2) adopt primarily the unsymmetric structure ArSnSn(H)2Ar in solution. Detailed theoretical calculations have been performed which include calculated UV-vis and IR spectra of various possible isomers of the reported hydrides and relevant model species. These showed that increased steric hindrance favors the asymmetric form ArSnSn(H)2Ar relative to the centrosymmetric isomer [ArSn(mu-H)]2 as a result of the widening of the interligand angles at tin, which lowers steric repulsion between the terphenyl ligands.     

Why the mechanisms of digermyne and distannyne reactions with H2 differ so greatly

Despite their formal relationship to alkynes, Ar'GeGeAr', Ar'SnSnAr', and Ar*SnSnAr* [Ar' = 2,6-(2,6-iPr(2)C(6)H(3))(2)C(6)H(3); Ar* = 2,6-(2,4,6-iPr(3)C(6)H(2))(2)-3,5-iPr(2)C(6)H] exhibit high reactivity toward H(2), quite unlike acetylenes. Remarkably, the products are totally different. Ar'GeGeAr' can react with 1-3 equiv of H(2) to give mixtures of Ar'HGeGeHAr', Ar'H(2)GeGeH(2)Ar', and Ar'GeH(3). In contrast, Ar'SnSnAr' and Ar*SnSnAr* react with only 1 equiv of H(2) but give different types of products, Ar'Sn(μ-H)(2)SnAr' and Ar*SnSnH(2)Ar*, respectively. In this work, this disparate behavior toward H(2) has been elucidated by TPSSTPSS DFT computations of the detailed reaction mechanisms, which provide insight into the different pathways involved. Ar'GeGeAr' reacts with H(2) via three sequential steps: H(2) addition to Ar'GeGeAr' to give singly H-bridged Ar'Ge(μ-H)GeHAr'; isomerization of the latter to the more reactive Ge(II) hydride Ar'GeGeH(2)Ar'; and finally, addition of another H(2) to the hydride, either at a single Ge site, giving Ar'H(2)GeGeH(2)Ar', or at a Ge-Ge joint site, affording Ar'GeH(3) + Ar'HGe:. Alternatively, Ar'Ge(μ-H)GeHAr' also can isomerize into the kinetically stable Ar'HGeGeHAr', which cannot react with H(2) directly but can be transformed to the reactive Ar'GeGeH(2)Ar'. The activation of H(2) by Ar'SnSnAr' is similar to that by Ar'GeGeAr'. The resulting singly H-bridged Ar'Sn(μ-H)SnHAr' then isomerizes into Ar'HSnSnHAr'. The subsequent facile dissociation of the latter gives two Ar'HSn: species, which then reassemble into the experimental product Ar'Sn(μ-H)(2)SnAr'. The reaction of Ar*SnSnAr* with H(2) forms in the kinetically and thermodynamically more stable Ar*SnSnH(2)Ar* product rather than Ar*Sn(μ-H)(2)SnAr*. The computed mechanisms successfully rationalize all of the known experimental differences among these reactions and yield the following insights into the behavior of the Ge and Sn species: (I) The active sites of Ar'EEAr' (E = Ge, Sn) involve both E atoms, and the products with H(2) are the singly H-bridged Ar'E(μ-H)EHAr' species rather than Ar'HEEHAr' or Ar'EEH(2)Ar'. (II) The heavier alkene congeners Ar'HEEHAr' (E = Ge, Sn) cannot activate H(2) directly. Instead, Ar'HGeGeHAr' must first isomerize into the more reactive Ar'GeGeH(2)Ar'. Interestingly, the subsequent H(2) activation by Ar'GeGeH(2)Ar' can take place on either a single Ge site or a joint Ge-Ge site, but Ar'SnSnH(2)Ar' is not reactive toward H(2). The higher reactivity of Ar'GeGeH(2)Ar' in comparison with Ar'SnSnH(2)Ar' is due to the tendency of group 14 elements lower in the periodic table to have more stable lone pairs (i.e., the inert pair effect) and is responsible for the differences between the reactions of Ar'EEAr' (E = Ge, Sn) with H(2). Similarly, the carbene-like Ar'HGe: is more reactive toward H(2) than is Ar'HSn:. (III) The doubly H-bridged Ar'E(μ-H)(2)EAr' (E = Ge, Sn) species are not reactive toward H(2).     

Formation of [Ar*Ge(CH2C(Me)C(Me)CH2)CH2C(Me)=]2 (Ar* = C6H3-2,6-Trip2; Trip = C6H2-2,4,6-i-Pr3) via reaction of Ar*GeGeAr* with 2,3-dimethyl-1,3-butadiene: evidence for the existence of a germanium analogue of an alkyne

The reduction of Ar*GeCl (Ar* = C6H3-2,6-Trip2; Trip = C6H2-2,4,6-i-Pr3) with one equivalent of potassium leads to the formation of a germanium analogue of an alkyne Ar*GeGeAr* 1; reaction of 1 with 2,3-dimethyl-1,3-butadiene yields [Ar*Ge(CH2C(Me)C(Me)CH2)CH2C(Me)=]2 2, which was structurally characterized.     

Boron-pnictogen multiple bonds: donor-stabilized P=B and As=B bonds and a hindered iminoborane with a B-N triple bond

Reaction of the hindered phosphino- and arsinoboranes, Ar*Pn(H)-B(Br)Tmp (Ar* = -C6H3-2,6-(C6H2-2,4,6-iPr3)2; Tmp = 2,2,6,6-tetramethylpiperidino; Pn = P and As, 1 and 3, respectively) with 4-dimethylaminopyridine, DMAP, afforded the boranylidenephosphane and arsane, Ar*Pn=B(DMAP)Tmp (Pn = P and As, 2 and 4) as deep red-purple solids. The analogous aminoboranes Ar'N(H)-B(X)Tmp (Ar' = -C6H3-2,6-(C6H2-2,4,6-Me3)2; X = Cl and Br; 5 and 6) did not display any reactivity with DMAP, but in the presence of the amide base, Na[N(SiMe3)2], the clean formation of the uncomplexed iminoborane Ar'NBTmp (7) was observed. Attempts to generate an Sb=B bond were unsuccessful, as the required stibinoborane precursor, Ar*Sb(H)-B(Br)Tmp, could not be prepared; in place of clean Sb-B bond formation, the reduced product Ar*Sb=SbAr* was obtained. All compounds were characterized spectroscopically, and the X-ray crystal structures of 1, 2, 4, 6, and 7 were determined.     

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.     

An arene-stabilized cobalt(I) aryl: reactions with CO and NO

The half-sandwich cobalt(I) complex (eta (6)-C 7H 8)CoAr*-3,5- ( i )Pr 2 (Ar*-3,5- ( i )Pr 2 = -C 6H-2,6-(C 6H 2-2,4,6- ( i )Pr 3) 2-3,5- ( i )Pr 2) was synthesized by reduction of [3,5- ( i )Pr 2Ar*Co(mu-Cl)] 2 in toluene. It reacts with CO or NO to afford the unusual complexes [3,5- ( i )Pr 2Ar*C(O)Co(CO)] or [3,5- ( i )Pr 2Ar*N(NO)OCo(NO) 2].     

Reversible and irreversible higher-order cycloaddition reactions of polyolefins with a multiple-bonded heavier group 13 alkene analogue: contrasting the behavior of systems with π-π, π-π*, and π-n+ frontier molecular orbital symmetry

The heavier group 13 element alkene analogue, digallene Ar(iPr(4))GaGaAr(iPr(4)) (1) [Ar(iPr(4)) = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)], has been shown to react readily in [n + 2] (n = 6, 4, 2 + 2) cycloaddition reactions with norbornadiene and quadricyclane, 1,3,5,7-cyclooctatetraene, 1,3-cyclopentadiene, and 1,3,5-cycloheptatriene to afford the heavier element deltacyclane species Ar(iPr(4))Ga(C(7)H(8))GaAr(iPr(4)) (2), pseudoinverse sandwiches Ar(iPr(4))Ga(C(8)H(8))GaAr(iPr(4)) (3, 3(iso)), and polycyclic compounds Ar(iPr(4))Ga(C(5)H(6))GaAr(iPr(4)) (4) and Ar(iPr(4))Ga(C(7)H(8))GaAr(iPr(4)) (5, 5(iso)), respectively, under ambient conditions. These reactions are facile and may be contrasted with other all-carbon versions, which require transition-metal catalysis or forcing conditions (temperature, pressure), or with the reactions of the corresponding heavier group 14 species Ar(iPr(4))EEAr(iPr(4)) (E = Ge, Sn), which give very different product structures. We discuss several mechanistic possibilities, including radical- and non-radical-mediated cyclization pathways. These mechanisms are consistent with the improved energetic accessibility of the LUMO of the heavier group 13 element multiple bond in comparison with that of a simple alkene or alkyne. We show that the calculated frontier molecular orbitals (FMOs) of Ar(iPr(4))GaGaAr(iPr(4)) are of π-π symmetry, allowing this molecule to engage in a wider range of reactions than permitted by the usual π-π* FMOs of C-C π bonds or the π-n(+) FMOs of heavier group 14 alkyne analogues.     

Substituent effects in formally quintuple-bonded ArCrCrAr compounds (Ar = terphenyl) and related species

The effects of different terphenyl ligand substituents on the quintuple Cr-Cr bonding in arylchromium(I) dimers stabilized by bulky terphenyl ligands (Ar) were investigated. A series of complexes, ArCrCrAr (1-4; Ar = C6H2-2,6-(C6H3-2,6-iPr2)2-4-X, where X = H, SiMe3, OMe, and F), was synthesized and structurally characterized. Their X-ray crystal structures display similar trans-bent C(ipso)CrCrC(ipso) cores with short Cr-Cr distances that range from 1.8077(7) to 1.8351(4) A. There also weaker Cr-C interactions [2.294(1)-2.322(2) A] involving an C(ipso) of one of the flanking aryl rings. The data show that the changes induced in the Cr-Cr bond length by the different substituents X in the para positions of the central aryl ring of the terphenyl ligand are probably a result of packing rather than electronic effects. This is in agreement with density functional theory (DFT) calculations, which predict that the model compounds (4-XC6H4)CrCr(C6H4-4-X) (X = H, SiMe3, OMe, and F) have similar geometries in the gas phase. Magnetic measurements in the temperature range of 2-300 K revealed temperature-independent paramagnetism in 1-4. UV-visible and NMR spectroscopic data indicated that the metal-metal-bonded solid-state structures of 1-4 are retained in solution. Reduction of (4-F3CAr')CrCl (4-F3CAr' = C6H2-2,6-(C6H3-2,6-iPr2)2-4-CF3) with KC8 gave non-Cr-Cr-bonded fluorine-bridged dimer {(4-F3CAr')Cr(mu-F)(THF)}2 (5) as a result of activation of the CF3 moiety. The monomeric, two-coordinate complexes [(3,5-iPr2Ar*)Cr(L)] (6, L = THF; 7, L = PMe3; 3,5-iPr2Ar* = C6H1-2,6-(C6H-2,4,6-iPr3)2-3,5-iPr2) were obtained with use of the larger 3,5-Pri2-Ar* ligand, which prevents Cr-Cr bond formation. Their structures contain almost linearly coordinated CrI atoms, with high-spin 3d5 configurations. The addition of toluene to a mixture of (3,5-iPr2Ar*)CrCl and KC8 gave the unusual dinuclear benzyl complex [(3,5-iPr2Ar*)Cr(eta3:eta6-CH2Ph)Cr(Ar*-1-H-3,5-iPr2)] (8), in which a C-H bond from a toluene methyl group was activated. The electronic structures of 5-8 have been analyzed with the aid of DFT calculations.     

Synthesis and characterisation of selected group 14 derivatives of the 2,5-(CF3)2C6H3 (Ar) ligand

Selected group 14 tetrahalides EX(4) (E = Si, Ge or Sn; X = Cl or Br) have been reacted in various molar ratios with ArLi, where Ar = 2,5-(CF(3))(2)C(6)H(3). The compounds Ar(2)SiCl(2)1, Ar(3)SiF 3, Ar(2)Si(OH)(2)4, Ar(2)GeCl(2)7, Ar(2)Ge(Br)Ge(Br)Ar(2)8, Ar(3)SnCl 10, Ar(4)Sn 11 and Ar(3)SnBr 12 have been isolated, and characterised by single-crystal X-ray diffraction, elemental analysis and (19)F solution-state NMR spectroscopy.     

Stannylplumbylenes: bonding between tetravalent tin and divalent lead

Depending on stoichiometry, reactions of the mixed valence Sn(0)/Sn(III) compound Sn(SnAr(3))(2) (1) (Ar = C(6)H(4)(O(i)Pr)(2)-2,6) with the likewise substituted plumbylene PbAr(2) (3) afforded either the homoleptic distannylplumbylene Pb(SnAr(3))(2) (4) or the heteroleptic arylstannylplumbylene Pb(Ar)SnAr(3) (5), a valence isomer of a stannaplumbene.     

Univalent transition metal complexes of arenes stabilized by a bulky terphenyl ligand: differences in the stability of Cr(I), Mn(I) or Fe(I) complexes

Two univalent transition metal complexes, (micro-eta6:eta6-C7H8){MnAr*-3,5-Pri2}2 () and (eta6-C6H6)FeAr*-3,5-Pri2 () (Ar*-3,5-Pri2=C6H-2,6-(C6H(2)-2,4,6-Pri3)(2)-3,5-Pri2), that have eta6 arene coordination were synthesized by reduction of the corresponding metal halides. The complexes are thermally stable in contrast to the corresponding Cri complexes of benzene or toluene which decompose at room temperature.     

A germanium isocyanide complex featuring (n → π*) back-bonding and its conversion to a hydride/cyanide product via C-H bond activation under mild conditions

Reaction of the diarylgermylene Ge(Ar(Me(6)))(2) [Ar(Me(6)) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-(CH(3))(3))(2)] with tert-butyl isocyanide gave the Lewis adduct species (Ar(Me(6)))(2)GeCNBu(t), in which the isocyanide ligand displays a decreased C-N stretching frequency consistent with an n → π* back-bonding interaction. Density functional theory confirmed that the HOMO is a Ge-C bonding combination between the lone pair of electrons on the germanium atom and the C-N π* orbital of the isocyanide ligand. The complex undergoes facile C-H bond activation to produce a new diarylgermanium hydride/cyanide species and isobutene via heterolytic cleavage of the N-Bu(t) bond.     

Lower homologues (methyl, ethyl) of diorganotin derivatives of germyl (substituted) propanoic acids: spectroscopic elucidations and biological studies

Some novel lower homologues of diorganotin derivatives of germyl substituted propanoic acids with general formula [Ar(3)GeCH(R(1))CH(R(2))COO](2)SnR(2)(3), where Ar = p-CH(3)C(6)H(4), C(6)H(5), R(1) = p-CH(3)C(6)H(4), p-CH(3)OC(6)H(4), o-CH(3)OC(6)H(4), C(6)H(5), R(2) = H, CH(3), R(3) = CH(3), C(2)H(5) have been prepared by the condensation reaction of dialkyltin oxide and triarylgermyl(substituted) propanoic acid in 1 : 2 M ratio, respectively, and were characterized by IR, multinuclear ((1)H, (13)C, (119)Sn) NMR, (119 m)Sn M?ssbauer spectroscopy. The synthesized compounds were also screened for their toxicity and possible antibacterial, antifungal activities and found some encouraging results.     

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.     

Pi-bonding encapsulation in aryl-substituted lanthanide selenolates: monomeric compounds with apparent low-coordinate metal atoms

Reaction of LnCl3 with KSeAr* in thf afforded the unsolvated, alkane-soluble complexes LnCl(SeAr*)2 (Ln = Nd, Pr; Ar* = 2,6-Trip(2)C(6)H(3); Trip = 2,4,6-iPr(3)C(6)H(2)) in which the rare-earth metal cations show additional eta6-pi-coordination by two flanking arene rings.     

C-H activation on a diphosphine and hydrido-bridged diiridium complex: generation and detection of an active IrII-IrII species [(Cp*Ir)2(micro-dmpm)(micro-H)]+

Reaction of [Cp*Ir(micro-H)](2) (5) (Cp* = eta(5)-C(5)Me(5)) with bis(dimethylphosphino)methane (dmpm) gives a new neutral diiridium complex [(Cp*Ir)(2)(micro-dmpm)(micro-H)(2)] (3). Treatment of 3 with methyl triflate at -30 degrees C results in the formation of [(Cp*Ir)(H)(micro-dmpm)(micro-H)(Me)(IrCp*)][OTf] (6). Warming a solution of above 0 degrees C brings about predominant generation of 32e(-) Ir(II)-Ir(II) species [(Cp*Ir)(micro-dmpm)(micro-H)(IrCp*)][OTf] (7). Further heating of the solution of 7 up to 30 degrees C for 14 h leads to quantitative formation of a new complex [(Cp*Ir)(H)(micro-Me(2)PCH(2)PMeCH(2))(micro-H)(IrCp*)][OTf] (8), which is formed by intramolecular oxidative addition of the methyl C-H bond of the dmpm ligand. Intermolecular C-H bond activation reactions with 7 are also examined. Reactions of 7 with aromatic molecules (benzene, toluene, furan, and pyridine) at room temperature result in the smooth sp(2) C-H activation to give [(Cp*Ir)(H)(micro-dmpm)(micro-H)(Ar)(IrCp*)][OTf] (Ar = Ph (9); Ar = m-Tol (10a) or p-Tol (10b); Ar = 2-Fur (11)) and [(Cp*Ir)(H)(micro-dmpm)(micro-C(5)H(4)N)(H)(IrCp*)][OTf] (12), respectively. Complex also reacts with cyclopentene at 0 degrees C to give [(Cp*Ir)(H)(micro-dmpm)(micro-H)(1-cyclopentenyl)(IrCp*)][OTf] (13). Structures of 3, 8 and 12 have been confirmed by X-ray analysis.     

Structures,bonding, and reaction chemistry of the neutral organogallium(I) compounds (GaAr)n(n = 1 or 2) (Ar = terphenyl or related ligand): an experimental investigation of Ga-Ga multiple bonding

The synthesis, structure, and properties of several new organogallium(I) compounds are reported. The monovalent compounds GaAr* (Ar* = C(6)H(3)-2,6-Trip(2), Trip = C(6)H(2)-2,4,6-Pr(i)()(3), 1), GaAr# (Ar# = C(6)H(3)-2,6(Bu(t)Dipp)(2), Bu(t)Dipp = C(6)H(2)-2,6-Pr(i)(2)-4-Bu(t)(), 4), and the dimeric (GaAr')(2) (Ar' = C(6)H(3)-2,6-Dipp(2), Dipp = C(6)H(3)-2,6-Pr(i)(2), 6) were synthesized by the reaction of "GaI" with (Et(2)O)LiAr*, (Et(2)O)LiAr# (3), or (LiAr')(2). Compounds 1 and 4 were isolated as green crystals, whereas 6 was obtained as a brown-red crystalline solid. All three compounds dissolved in hydrocarbon solvents to give green solutions and almost identical UV/visible spectra. Cryoscopy of 1 and 6 showed that they were monomeric in cyclohexane. Crystals of 1 and 4 were unsuitable for X-ray crystal structure determinations, but an X-ray data set for 6 showed that it was weakly dimerized in the solid with a long Ga-Ga bond of 2.6268(7) A and a trans-bent CGaGaC core array. The 1,2-diiodo-1,2-diaryldigallane compounds [Ga(Ar*)I](2) (2), [Ga(Ar#)I](2) (5), and [Ga(Ar')I](2) (7) were isolated as byproducts of the synthesis of 1, 4, and 6. The crystal structures of 2 and 7 showed that they had planar ICGaGaCI core arrays with Ga-Ga distances near 2.49 A, consistent with Ga-Ga single bonding. Treatment of 1, 4, and 6 with B(C(6)F(5))(3) immediately afforded the 1:1 donor-acceptor complexes ArGa[B(C(6)F(5))(3)] (Ar = Ar*, 8; Ar#, 9; Ar', 10) that featured almost linear gallium coordination, Ga-B distances near the sum of the covalent radii of gallium and boron, as well as some close Ga...F contacts. Compound 1 also reacted with Fe(CO)(5) under ambient conditions to give Ar*GaFe(CO)(4) (11), which had been previously synthesized by the reaction of GaAr*Cl(2) with Na(2)Fe(CO)(4). Reaction of 1 with 2,3-dimethyl-1,3-butadiene afforded the compound [Ar*GaCH(2)C(Me)C(Me)CH(2)]2 (12) that had a 10-membered 1,5-Ga(2)C(8) ring with no Ga-Ga interaction. Stirring 1 or 6 with sodium readily gave Na(2)[Ar*GaGaAr*] (13) and Na(2)(Ar'GaGaAr') (14). The former species 13 had been synthesized previously by reduction of GaAr*Cl(2) with sodium and was described as having a Ga-Ga triple bond because of the short Ga-Ga distance and the electronic relationship between [Ar*GaGaAr*](2-) and the corresponding neutral group 14 alkyne analogues. Compound 14 has a similar structure featuring a trans-bent CGaGaC core, bridged by sodiums which were also coordinated to the flanking aryl rings of the Ar' ligands. The Ga-Ga bond length was found to be 2.347(1) A, which is slightly (ca. 0.02 A) longer than that reported for 13. Reaction of Ga[N(Dipp)C(Me)](2)CH, 15 (i.e., GaN(wedge)NDipp(2)), which is sterically related to 1, 4, and 6, with Fe(CO)(5) yielded Dipp(2)N(wedge)NGaFe(CO)(4) (16), whose Ga-Fe bond is slightly longer than that observed in 11. Reaction of the less bulky LiAr"(Ar"= C(6)H(3)-2,6-Mes(2)) with "GaI" afforded the new paramagnetic cluster Ga(11)Ar(4)" (17). The ready dissociation of 1, 4, and 6 in solution, the long Ga-Ga distance in 6, and the chemistry of these compounds showed that the Ga-Ga bonds are significantly weaker than single bonds. The reduction of 1 and 6 with sodium to give 13 and 14 supplies two electrons to the di-gallium unit to generate a single bond (in addition to the weak interaction in the neutral precursor) with retention of the trans-bent geometry. It was concluded that the stability of 13 and 14 depends on the matching size of the sodium ion, and the presence of Na-Ga and Na-Ar interactions that stabilize their Na(2)Ga(2) core structures.     

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.     

Terphenyl substituted derivatives of manganese(II): distorted geometries and resistance to elimination

Reaction of {Li(THF)Ar'MnI(2)}(2) (Ar' = C(6)H(3)-2,6-(C(6)H(2)-2,6-(i)Pr(3))(2)) with LiAr', LiC≡CR (R = (t)Bu or Ph), or (C(6)H(2)-2,4,6-(i)Pr(3))MgBr(THF)(2) afforded the diaryl MnAr'(2) (1), the alkynyl salts Ar'Mn(C≡C(t)Bu)(4){Li(THF)}(3) (2) and Ar'Mn(C≡CPh)(3)Li(3)(THF)(Et(2)O)(2)(μ(3)-I) (3), and the manganate salt {Li(THF)}Ar'Mn(μ-I)(C(6)H(2)-2,4,6-(i)Pr(3)) (4), respectively. Complex 4 reacted with one equivalent of (C(6)H(2)-2,4,6-(i)Pr(3))MgBr(THF)(2) to afford the homoleptic dimer {Mn(C(6)H(2)-2,4,6-(i)Pr(3))(μ-C(6)H(2)-2,4,6-(i)Pr(3))}(2) (5), which resulted from the displacement of the bulkier Ar' ligand in preference to the halogen. The reaction of the more crowded {Li(THF)Ar*MnI(2)}(2) (Ar* = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-(i)Pr(3))(2)) with Li(t)Bu gave complex Ar*Mn(t)Bu (6). Complex 1 is a rare monomeric homoleptic two-coordinate diaryl Mn(II) complex; while 6 displays no tendency to eliminate β-hydrogens from the (t)Bu group because of the stabilization supplied by Ar*. Compounds 2 and 3 have cubane frameworks, which are constructed from a manganese, three carbons from three acetylide ligands, three lithiums, each coordinated by a donor, plus either a carbon from a further acetylide ligand (2) or an iodide (3). The Mn(II) atom in 4 has an unusual distorted T-shaped geometry while the dimeric 5 features trigonal planar manganese coordination. The chloride substituted complex Li(2)(THF)(3){Ar'MnCl(2)}(2) (7), which has a structure very similar to that of {Li(THF)Ar'MnI(2)}(2), was also prepared for use as a possible starting material. However, its generally lower solubility rendered it less useful than the iodo salt. Complexes 1-7 were characterized by X-ray crystallography and UV-vis spectroscopy. Magnetic studies of 2-4 and 6 showed that they have 3d(5) high-spin configurations.