Trigonal Pyramidal Geometry Research Articles

One- and two-dimensional cobalt(II) coordination polymers derived from flexible bis(benzimidazole) and aromatic carboxylate co-ligands

Two new coordination polymers, formulated as [Co(L1)(btec)0.5] n (1) and {[Co(L2)(bdc)]·H2O} n (2) (L1 = 1,3-bis(2-methylbenzimidazol-1-ylmethyl)benzene, H2bdc = 1,3-benzenedicarboxylic acid, H4btec = 1,2,4,5-benzenetetracarboxylic acid, L2 = 1,3-bis(benzimidazol-1-ylmethyl)benzene), have been hydrothermally synthesized and characterized by physicochemical and spectroscopic methods as well as single-crystal X-ray diffraction. The cobalt atoms present different environments, with a trigonal pyramidal geometry in 1 and a distorted octahedral configuration in 2. Complex 1 shows a 2D (4,4) network linked by L1 and btec4− anions, giving an uninodal 4-connected sql topology with a point symbol of {42·62}, while complex 2 displays a 1D ladder-like chain structure, which is further assembled into a 3D supramolecular architecture via C–H···π hydrogen bonding interactions. The fluorescence properties of both complexes have been investigated in the solid state.

Synthesis and Characterization of Aluminum-α-diimine Complexes over Multiple Redox States

The aluminum complexes (LMes(2-))AlCl(THF) (3) and (LDipp(-))AlCl2 (4) (LMes = N,N'-bis[2,4,6-trimethylphenyl]-2,3-dimethyl-1,4-diazabutadiene, LDipp = N,N'-bis[2,6-diisopropylphenyl]-2,3-dimethyl-1,4-diazabutadiene) were prepared by direct reduction of the ligands with sodium metal followed by salt metathesis with AlCl3. The (LMes(-))AlCl2 (5) complex was prepared through one-electron oxidative functionalization of 3 with either AgCl or CuCl. Complex 3 was characterized using (1)H and (13)C NMR spectoscopies. Single-crystal X-ray diffraction analysis of the complexes revealed that 3-5 are all four-coordinate, with 3 exhibiting a trigonal pyramidal geometry, while 4 and 5 exist between trigonal pyramidal and tetrahedral. Notable in the LMes complexes 3 and 5 is a systematic lengthening of the C-Nimido bonds and shortening of the C-C bond in the N-C-C-N backbone with increased electron density on the ligand. The geometries of the complexes 3 and 5 were optimized using DFT, which showed primarily ligand-based frontier orbitals, supporting the analysis of the solid-state structural data. The complexes 3-5 were also characterized by electrochemistry. The cyclic voltamogram of complex 3 showed an oxidation processes at -0.94 and -0.03 V versus ferrocene, while complexes 4 and 5 exhibit both reduction (-1.37 and -1.34 V, respectively) and oxidation (-0.62 and -0.73 V, respectively) features.

Five new mononuclear zinc(II) complexes with a tetradentate N-donor Schiff base: Syntheses, structures and influence of anionic coligands on the luminescence behaviour and supramolecular interactions

The present report describes the syntheses, structures and luminescence properties of five mononuclear complexes, [Zn(L)Cl]ClO4 (1), [Zn(L)Br]ClO4 (2), [Zn(L)I]ClO4 (3), [Zn(L)N3]ClO4 (4), and [Zn(L)(NCS)](SCN) (5), derived from the tetradentate ligand L, N,N′-bis(2-pyridylmethylene)-1,3-propanediamine. The geometry around the Zn2+ centre is best described as square pyramidal, although significant distortion towards the trigonal pyramidal geometry is noticed, especially for the halide complexes, of the later, the chloro (1) and bromo (2) complexes are isostructural and isomorphous. The stabilization of the crystal lattices is maintained by interesting, relatively strong hydrogen bonds and π⋯π interactions which lead to various supramolecular architectures. All the five complexes show photoluminescence properties and their trend can be correlated with the position of the apical anionic coligands in the spectrochemical series of ligands.

New Heteronuclear Bridged Borylene Complexes That Were Derived from [{Cp*CoCl}2] and Mono‐MetalCarbonyl Fragments

The synthesis, structural characterization, and reactivity of new bridged borylene complexes are reported. The reaction of [{Cp*CoCl}2] with LiBH4·THF at -70 °C, followed by treatment with [M(CO)3(MeCN)3] (M=W, Mo, and Cr) under mild conditions, yielded heteronuclear triply bridged borylene complexes, [(μ3-BH)(Cp*Co)2(μ-CO)M(CO)5] (1-3; 1: M=W, 2: M=Mo, 3: M=Cr). During the syntheses of complexes 1-3, capped-octahedral cluster [(Cp*Co)2(μ-H)(BH)4{Co(CO)2}] (4) was also isolated in good yield. Complexes 1-3 are isoelectronic and isostructural to [(μ3-BH)(Cp*RuCO)2(μ-CO){Fe(CO)3}] (5) and [(μ3-BH)(Cp*RuCO)2(μ-H)(μ-CO){Mn(CO)3}] (6), with a trigonal-pyramidal geometry in which the μ3-BH ligand occupies the apical vertex. To test the reactivity of these borylene complexes towards bis-phosphine ligands, the room-temperature photolysis of complexes 1-3, 5, 6, and [{(μ3-BH)(Cp*Ru)Fe(CO)3}2(μ-CO)] (7) was carried out. Most of these complexes led to decomposition, although photolysis of complex 7 with [Ph2P(CH2)(n)PPh2] (n=1-3) yielded complexes 9-11, [3,4-(Ph2P(CH2)(n)PPh2)-closo-1,2,3,4-Ru2Fe2(BH)2] (9: n=1, 10: n=2, 11: n=3). Quantum-chemical calculations by using DFT methods were carried out on compounds 1-3 and 9-11 and showed reasonable agreement with the experimentally obtained structural parameters, that is, large HOMO-LUMO gaps, in accordance with the high stabilities of these complexes, and NMR chemical shifts that accurately reflected the experimentally observed resonances. All of the new compounds were characterized in solution by using mass spectrometry, IR spectroscopy, and (1)H, (13)C, and (11)B NMR spectroscopy and their structural types were unequivocally established by crystallographic analysis of complexes 1, 2, 4, 9, and 10.

Organoantimony(III) and -bismuth(III) hypervalent pseudohalides. An experimental and theoretical study

The reaction between the organopnicogen(III) chlorides R2MCl and RMCl2 [M = Sb, Bi; R = 2-(Me2NCH2)C6H4] and alkali metal pseudohalides in a 1:1 and a 1:2 molar ratio, respectively, resulted in the formation of hypervalent species of type R2MX (M = Sb, X = NCO (1), NCS (2) and SeCN (3), M = Bi, X = NCO (4) and SeCN (5), and RMX2 (M = Sb, X = NCO (6) and NCS (7), M = Bi, X = NCO (8), NCS (9) and SeCN (10). The new species were characterized by multinuclear NMR (1H, 13C, 77Se where appropriate), IR spectroscopy and mass spectrometry. The molecular structures of compounds 2–5 and 7 were determined by single-crystal X-ray diffraction. In all five compounds the nitrogen atoms in the pendant arms are involved in intramolecular coordination to metal, thus resulting in a distorted square pyramidal coordination geometry (12-M-5 hypervalent species) in case of 2–5 and a distorted trigonal pyramidal coordination geometry in case of 7 (10-Sb-4 hypervalent species). The intramolecular N → M coordination determines a chiral pattern of the investigated compounds. Bi⋯Phcentroid intermolecular interactions led to dimers in case of compound 4. In all species weak CH⋯Phcentroid intermolecular contacts led to polymeric associations, e.g. polymeric chains in case of compounds 2, 3, 5 and 7 and a 2D layer structure built by chains of dimers in case of compound 4. DFT calculations and FTIR data allowed us to assign the coordination pattern of the pseudohalide ligand in the other species.

Tris(μ4-azepane-1-carbodithioato)bis(μ3-azepane-1-carbodithioato)-μ9-bromido-tetra-μ2-bromido-octacopper(I)copper(II)

The reaction of Cu(Hm-dtc)2 (H2m-dtc is azepane-1-carbodi­thioic acid), CuBr2 and methyl iso­thio­cyanate yielded the title mixed-valence nona­nuclear CuI/CuII compound, [Cu9Br5(C7H12NS2)5] or [CuI 8CuIIBr5(Hm-dtc)5], encapsulating a bromide anion in the center of the Cu9Br4S10 cluster cage. The cage consists of a mononuclear CuII unit [Cu(Hm-dtc)2], three μ4-bridging Hm-dtc− ligands, eight CuI ions with distorted tetra­hedral or trigonal pyramidal coordination geometries and four μ2-bridging bromide anions. The incorporated central bromide anion inter­acts with nine Cu ions with shorter Cu—Br separations than the sum of the van der Waals radii for Cu and Br.

Rac-(1S*,4aS*,8aS*)-4a-Hydroxy-2-methylperhydrospiro[isoquinoline-4,1′-cyclohexan]-2′-one

In the title compound, C15H25NO2, all three six-membered rings adopt chair conformations. The cyclo­hexane and piperidine rings within the perhydro­isoquinoline are trans–trans fused. The N atom has a trigonal–pyramidal geometry (the sum of the bond angles is 328.0°). The methyl substituent occupies the sterically preferrable equatorial position. In the crystal, mol­ecules form infinite [100] chains via O—H⋯N hydrogen bonds.

Structural characterization of tris(pyrazolyl)hydroborato and tris(2-pyridylthio)methyl lithium compounds: Lithium in uncommon trigonal pyramidal and trigonal monopyramidal coordination environments

X-ray diffraction reveals that the molecular structures of the tris(pyrazolyl)hydroborato and tris(2-pyridylthio)methyl lithium compounds, [TpBut,R]Li (R=H, Me) and [κ4-Tptm]Li, respectively exhibit three-coordinate trigonal pyramidal and four-coordinate trigonal monopyramidal coordination geometries, both of which are uncommon for lithium. Accordingly, [TpBut]Li and [TpBut,Me]Li bind additional ligands to form four-coordinate adducts, such as [TpBut]Li(NCMe), [TpBut,Me]Li(NCMe), [TpBut]Li(pzButH), [TpBut,Me]Li(pzButH)·(pzButH), [TpBut,Me]Li(OH2), [TpBut,Me]Li(OH2)·(pzH) and [TpBut]Li(OH2)·(THF), each of which has been structurally characterized by X-ray diffraction in the solid state. In solution, however, dissociation of the ligand (L) from the adducts [TpBut,R]LiL is facile such that the adducts exist in equilibrium with [TpBut,R]Li and L, as demonstrated by NMR spectroscopic studies.

Syntheses of bis(pyrrolylaldiminato)aluminum complexes for the polymerisation of lactide

Seven bis(pyrrolylaldiminato)aluminum methyl complexes were synthesized from the reactions of AlMe3 and two equiv. of the corresponding pyrrolylaldimine ligands. The ligands were modified to have different steric hindrances (C6H5 (1), 2,6-Me2C6H3 (2), 2,4,6-Me3C6H2 (3), 2,6-Et2C6H3 (4) and 2,6-(i)Pr2C6H3 (5)) and electronic contributions (4-CF3C6H4 (6) and 4-OMeC6H4 (7)). Crystal structures of complexes 3-7 were determined and shown to have distorted trigonal bipyramidal geometry (4, 6, 7) and intermediates between trigonal bipyramidal and square pyramidal geometries (3 and 5). The rotation around the N-C(aryl) bond was fast for ligands having small ortho substituents and became slower as the size of the substituents increased. Polymerisations of l-lactide using complexes 1-7 and benzyl alcohol as an initiator were carried out giving the rate dependence on steric hindrance (5 < 4 < 3 < 2 < 1) and electronic contribution (6 < 7 < 1). Larger substituents and electron withdrawing groups were found to suppress the polymerisation rates. Despite having C2 symmetry in the crystal structures of compounds 3-7, only slight enhancement for isotactic enchainment was found in the polymerisation of rac-lactide.

Anti-leishmanial activity of heteroleptic organometallic Sb(v) compounds

In seeking new drugs for the treatment of the parasitic disease Leishmaniasis, an extensive range of organometallic antimony(v) dicarboxylates of the form [SbR3(O2CR')2] have been synthesised, characterised and evaluated. The organometallic moieties (R) in the complexes vary in being Ph, tolyl (o, m or p), or benzyl. The carboxylates are predominantly substituted benzoates with some compounds incorporating acetato or cinnamato ligands. The crystal structures of [Sb(p-Tol)3(O2CC6H2-3,4,5-(OMe)3)2]·0.5PhMe and [SbPh3(m-CH3C6H4CH2CO2)2] were determined and shown to adopt a typical trigonal pyramidal geometry, being monomeric with a five coordinate Sb centre. In total, the biological activity of 26 Sb(v) compounds was assessed against the Leishmania major parasite, and also human fibroblast skin cells to give a measure of general toxicity. Of these, 11 compounds (predominantly substituted benzoates with m- or p-tolyl ligands) proved to be highly effective against the parasite amastigotes at concentrations of 0.5-3.5 μM, while being non-toxic towards the mammalian cells at levels below 25 μM, making them highly promising drug candidates.

Synthesis and characterization of a family of Co(II) triphenylamido-amine complexes and catalytic activity in controlled radical polymerization of olefins

The present work reports a new family of tripodal CoII complexes bearing trianionic triphenylamido-amine ligands with a variety of pendant arms (aryl, acyl, alkyl). These complexes have been synthesized by the reaction of anhydrous CoCl2 with the deprotonated ligands and exhibit stoichiometric and structural variation. The solid-state structures of these compounds reveal that in all cases the four nitrogen-atom residues of the ligands are coordinated to the metal center in a distorted trigonal-pyramidal geometry. In two cases, the presence of acetonitrile adds a fifth moiety to the coordination sphere. Among the aryl-armed CoII reagents, [K(L3)CoII–NCMe]n (1), [K(THF)6][(L5)CoII]·1.5THF (2) and [K(NCMe)3(L13)CoII–NCMe] (6), the two five-coordinate structures (1, 6) exhibit distorted trigonal bipyramidal geometries, with that of 6 being the least distorted. The four-coordinate species 2 is the only compound with a distinct anionic [(L5)CoII]− component, since the K+ ion is solely coordinated by solvent molecules. The acyl-armed CoII compounds [K(THF)2(L8)CoII]n (3) and {[K2(DMA)3(L10)2CoII2]·0.5Et2O}n (5) are strictly four-coordinate species, with the carbonyl moieties oriented exo with respect to the cavity of the vacant coordination site. Finally, compound [K2(L9)2CoII2]n (4) is the only example bearing an alkyl-armed ligand, and exhibits a geometry featuring a repeating –[Co(1)–K(1)–Co(2)–K(2)]n– sequence. All compounds have been characterized by spectroscopic and electrochemical techniques. Compounds 1, 2, 4, and 6 show reversible or semi-reversible CoII/CoIII redox couples, whereas the electron-deficient complexes 3 and 5 exhibit irreversible anodic waves. The catalytic reactivity of these complexes towards controlled radical polymerization (CRP) of styrene (St) and methyl methacrylate (MMA) has been studied and preliminary results are presented. Compounds 4 and 5 seem to be the most reactive with both monomers, giving high yields of polymers (60–86%), 3 efficiently induces styrene polymerization (90%), whereas 2 and 6 provide lower yields (12–16% for PS and 30–45% for PMMA). The steric factor seems to play an essential role, since CoII compounds that feature a less hindered fifth coordination site show the highest reactivity and better control over polymerization. The polymers obtained are predominately syndiotactic, consistent with radical polymerization, with two exceptions (1, 2) that exhibit unusually high ratios of isotactic triads. Interestingly, in many cases, the polymers obtained feature bimodal distributions, while the molecular weight distributions are not very broad (1.40–2.00), and this strongly indicates that two parallel mechanisms may be in operation.

3-Methyl-1,2,3,4,5,6,1′,2′,3′,4′-decahydrospiro[benz[f]isoquinoline-1,2′-naphthalen]-1′-one

The title compound, C23H23NO, is the product of a tandem transformation of the double Mannich base bis­(1-oxo-1,2,3,4-tertrahydro-2-naphtho­ylmeth­yl)amine hydro­chloride in HBr solution upon heating. The tetra­hydro­pyridine ring has a non-symmetrical half-chair conformation, whereas the cyclo­hexa­diene and cyclo­hexene rings adopt non-symmetrical half-boat conformations. The dihedral angle between the planes of the terminal benzene rings is 62.85 (6)°. The N atom has a trigonal–pyramidal geometry [sum of the bond angles = 332.4 (3)°]. In the crystal, mol­ecules form [001] chains via weak non-classical C—H⋯N hydrogen bonds. The chains are stacked along the b axis.

Isolation and X-ray structures of four Rh(PCP) complexes including a Rh(I) dioxygen complex with a short O–O bond

The reaction of RhCl3·H2O with tBu2P(CH2)5PtBu2 afforded several complexes including [RhIII(H)Cl{tBu2P(CH2)2CH(CH2)2PtBu2}] (1), [RhIIIHCl2{tBu2P(CH2)5PtBu2}]2 (2), [RhICl{tBu2P(CH2)2CHCHCH2PtBu2}] (3) and [RhICl{tBu2PCH2C(O)CHCHCH2PtBu2}] (4). X-ray crystal structures of 3 and 4 showed that the CC bond on the C5 unit of tBu2P(CH2)5PtBu2 is bound to Rh(I) in a η2 configuration. In 4, the Rh atom has a trigonal pyramidal coordination geometry. The X-ray crystal structure of 2 consists of two rhodium(III) centers bridged by two tBu2P(CH2)5PtBu2 ligands with two phosphorus atoms, one from each ligand, trans to one another. The crystal structure of the rhodium oxygen adduct with 1,3-bis(di-t-butylphosphinomethyl)benzene [RhO2{tBu2PCH2(C6H3)CH2PtBu2}] (5) was also investigated. In this species the O2 is η2 coordinated to the Rh(I) center with asymmetric Rh–O bond lengths (2.087(7) and 1.998(8)Å). The O–O bond distance is short (1.337(11)Å) with νO–O of 990.5cm−1. DFT calculations on complex 5 yielded two η2–O2 structures that differed in energy by only 0.76kcal/mol. The lower energy one (5a) had near C2 symmetry, and had nearly equal Rh–O bond lengths, while the higher energy structure (5b) had near Cs symmetry and generally good agreement with the experimental structure. The calculated UV–Vis and IR spectra of complex 5 are in excellent agreement with experiment.

Aminotroponiminatogermaacid Halides with a Ge(E)X Moiety (E = S, Se; X = F, Cl)

Fluorination of aminotroponiminate (ATI) ligand-stabilized germylene monochloride [(t-Bu)(2)ATI]GeCl (1) with CsF gave the aminotroponiminatogermylene monofluoride [(t-Bu)(2)ATI]GeF (2). Oxidative addition reaction of compound 2 with elemental sulfur and selenium led to isolation of the corresponding germathioacid fluoride [(t-Bu)(2)ATI]Ge(S)F (3) and germaselenoacid fluoride [(t-Bu)(2)ATI]Ge(Se)F (4), respectively. Similarly, reaction of aminotroponiminatogermylene monochloride [(i-Bu)(2)ATI]GeCl (9) with elemental sulfur and selenium gave the aminotroponiminatogermathioacid chloride [(i-Bu)(2)ATI]Ge(S)Cl (11) and aminotroponiminatogermaselenoacid chloride [(i-Bu)(2)ATI]Ge(Se)Cl (12), respectively. Compound 9 has been prepared through a multistep synthetic route starting from 2-(tosyloxy)tropone 5. All compounds (2-4 and 6-12) were characterized through the multinuclear NMR spectroscopy, and single-crystal X-ray diffraction studies were performed on compounds 2, 4, and 8-12. The germaselenoacid halide complexes 4 and 12 showed doublet (-142.37 ppm) and singlet (-213.13 ppm) resonances in their (77)Se NMR spectra, respectively. Germylene monohalide complexes 2 and 9 have a germanium center in distorted trigonal pyramidal geometry, whereas a distorted tetrahedral geometry is seen around the germanium center in germaacid halide complexes 4, 11, and 12. The length of the Ge═E bond in germathioacid chloride (11) and germaselenoacid halide (4 and 12) complexes is 2.065(1) and 2.194(av) Å, respectively. Theoretical studies (based on the DFT methods) on complexes 4, 11, and 12 reveal the nature of the Ge═E multiple bond in these germaacid halide complexes with computed Wiberg bond indices (WBI) being 1.480, 1.508, and 1.541, respectively.

Magnesium Cyclam complexes with a Mg2(Bn2Cyclam) core: Structural characterization of Mg2(Bn2Cyclam)I2 and Mg2(Bn2Cyclam){μ-H}{μ-F-C6F4}2BC6F5

This work describes the crystal structures of two Mg dimers supported by dianionic trans-disubstituted Bn2Cyclam ligands (1,8-dibenzyl-1,4,8,11-tetraazacyclotetradecane). Mg2(Bn2Cyclam)I2 (1) crystallizes in the monoclinic space group P21/c with half-molecule in the asymmetric unit. The two metal centers and the two Namido donors of the cyclam ring define a four-member Mg2N2 metallacycle. The metals’ coordination spheres are completed by one amine of the macrocycle and one iodide defining a trigonal pyramidal coordination geometry. Mg2(Bn2Cyclam){μ-H}{μ-F-C6F4}2BC6F5 (2) crystallizes in the monoclinic space group P21/c with half-molecule in the asymmetric unit. Compound 2 is a rare example of a zwitterionic species of the type [Mg2(Bn2Cyclam)]2+ with two [HB(C6F5)3]− anions coordinating in a k3-H,F,F tridentate fashion. This compound also displays bridging Namido ligands that bind the two Mg atoms in a Mg2N2 arrangement analogous to 1, promoting a capped square pyramidal coordination geometry. At a supramolecular level C–H⋯I and C–H⋯F hydrogen bonds as well as CH/π and F⋯F interactions are responsible for the crystal packing.

(N,N,N′,N′-Tetramethylethylenediamine-κN)bis(2,4,6-trimethylphenolato-κO)germanium(II)

In the title compound, [Ge(C9H11O)2(C6H16N2)], the GeII atom is coordinated in a distorted trigonal–pyramidal geometry by two O atoms belonging to two 2,4,6-trimethyl­phenolate ligands and one N atom of a tetra­methyl­ethylenediamine ligand. Comparing the structure with published data of similar compounds shows that the Ge—O bonds are covalent and the Ge—N bond is coordinated.

{μ-2-[4-(1,3-Benzothiazol-2-yl)phenyl]-2-azapropane-1,3-dithiolato-κ4S,S′:S,S′}bis[tricarbonyliron(I)

The title compound, [Fe2(C15H12N2S3)(CO)6], was prepared as an aza­dithiol­atodiiron model for the active site of [FeFe]-hydrogenase. The Fe2S2 core adopts a butterfly shape, with each metal having a pseudo square-pyramidal geometry. The N-substituted aza­dithiol­ate is μ2-κ4 S,S′:S,S′-coordinated to the Fe(CO)3 moieties to form two fused six-membered rings with different conformations. The sum of the C—N—C angles around the N atom [356.85 (15)°] indicates a flattening of the trigonal–pyramidal geometry about the N atom and an increase in the degree of sp 2-hybridization.

Complexes of Cu(i) supported by a tris(ketimine) tripod

Arylation of tris(2-benzylnitrile)amine with PhLi, followed by aqueous work-up, results in the formation of a tripodal tris(ketimine) scaffold, N(ArCNHPh)(3). N(ArCNHPh)(3) readily coordinates a number of Cu(I) salts, generating complexes that exhibit trigonal pyramidal geometries in the solid-state.

Four-Coordinate, 14-Electron RuII Complexes: Unusual Trigonal Pyramidal Geometry Enforced by Bis(phosphino)silyl Ligation

Unprecedented diamagnetic, four-coordinate, formally 14-electron (Cy-PSiP)RuX (Cy-PSiP = [κ(3)-(2-R(2)PC(6)H(4))(2)SiMe](-); X = amido, alkoxo) complexes that do not require agostic stabilization and that adopt a highly unusual trigonal pyramidal coordination geometry are reported. The tertiary silane [(2-Cy(2)PC(6)H(4))(2)SiMe]H ((Cy-PSiP)H) reacted with 0.5 [(p-cymene)RuCl(2)](2) in the presence of Et(3)N and PCy(3) to afford [(Cy-PSiP)RuCl](2) (1) in 74% yield. Treatment of 1 with KO(t)Bu led to the formation of (Cy-PSiP)RuO(t)Bu (2, 97% yield), which was crystallographically characterized and shown to adopt a trigonal pyramidal coordination geometry in the solid state. Treatment of 1 with NaN(SiMe(3))(2) led to the formation of (Cy-PSiP)RuN(SiMe(3))(2) (3, 70% yield), which was also found to adopt a trigonal pyramidal coordination geometry in the solid state. The related anilido complexes (Cy-PSiP)RuNH(2,6-R(2)C(6)H(3)) (4, R = H; 5, R = Me) were also prepared in >90% yields by treating 1 with LiNH(2,6-R(2)C(6)H(3)) (R = H, Me) reagents. The solid state structure of 5 indicates a monomeric trigonal pyramidal complex that features a C-H agostic interaction. Complexes 2 and 3 were found to react readily with 1 equiv of H(2)O to form the dimeric hydroxo-bridged complex [(Cy-PSiP)RuOH](2) (6, 94% yield), which was crystallographically characterized. Complexes 2 and 3 also reacted with 1 equiv of PhOH to form the new 18-electron η(5)-oxocyclohexadienyl complex (Cy-PSiP)Ru(η(5)-C(6)H(5)O) (7, 84% yield). Both amido and alkoxo (Cy-PSiP)RuX complexes reacted with H(3)B·NHRR' reagents to form bis(σ-B-H) complexes of the type (Cy-PSiP)RuH(η(2):η(2)-H(2)BNRR') (8, R = R' = H; 9, R = R' = Me; 10, R = H, R' = (t)Bu), which illustrates that such four-coordinate (Cy-PSiP)RuX (X = amido, alkoxo) complexes are able to undergo multiple E-H (E = main group element) bond activation steps. Computational methods were used to investigate structurally related PCP, PPP, PNP, and PSiP four-coordinate Ru complexes and confirmed the key role of the strongly σ-donating silyl group of the PSiP ligand set in enforcing the unusual trigonal pyramidal coordination geometry featured in complexes 2-5, thus substantiating a new strategy for the synthesis of low-coordinate Ru species. The mechanism of the activation of ammonia-borane by such low-coordinate (R-PSiP)RuX (X = amido, alkoxo) species was also studied computationally and was determined to proceed most likely in a stepwise fashion via intramolecular deprotonation of ammonia and subsequent borane B-H bond oxidative addition steps.

Lewis Base Complexes of an Enantiomeric Germanium(II) Cation Bearing a Bis(oxazoline) Ligand

A tetrahydrofuran (THF) complex of an enantiomeric germanium(II) cation functionalized by an anionic bis(oxazoline) ligand was synthesized in a mixture of dimethoxyethane (DME) and THF by abstraction of the chloride ion from the corresponding chlorogermylene. The coordinated THF was exchanged with the Lewis bases phosphine and pyridine at the same coordination site. X-ray crystallographic analysis revealed that the Lewis bases donate to a vacant p orbital of the germanium atom to form a trigonal-pyramidal geometry with a lone pair of electrons.