Heavier Group 13 Metal(I) Heterocycles Stabilized by Sterically Demanding Diiminophosphinates: A Structurally Characterized Monomer-Dimer Pair For Gallium.

We have synthesized and characterized the monomeric diiminophosphinate-stabilized Group 13 metal(I) complexes [Dip LE:], Dip L=Ph2 P(NDip)2 , Dip=2,6-iPr2 C6 H3 ; E=Ga (1), In (2) and Tl (3). In addition, we structurally characterized the dimeric complex [(Dip LGa)2 ], 12 . Similar synthetic attempts using Mes L=Ph2 P(NMes)2 , Mes=2,4,6-Me3 C6 H2 afforded product mixtures from which the mixed oxidation state species [(Mes L)3 Ga4 I3 ] 4 was isolated. [Dip LGa:] 1 is converted with dry air to the gallium(III) oxide species [(Dip LGaO)2 ] 5. Density Functional Theory studies on [Dip LE:] and [(Dip LE)2 ], E=Al-Tl, shed light on the bonding in these compounds and show that the newly formed E-E bonding interactions can be described as weak single σ-bond with no significant π-bonding contribution for E=Al, Ga. A large contribution to the dimer binding enthalpies results from London dispersion forces.

Ring-Shaped Phosphinoamido-Magnesium-Hydride Complexes: Syntheses, Structures, Reactivity, and Catalysis.

A series of magnesium(II) complexes bearing the sterically demanding phosphinoamide ligand, L(-) =Ph2 PNDip(-) , Dip=2,6-diisopropylphenyl, including heteroleptic magnesium alkyl and hydride complexes are described. The ligand geometry enforces various novel ring and cluster geometries for the heteroleptic compounds. We have studied the stoichiometric reactivity of [(LMgH)4 ] towards unsaturated substrates, and investigated catalytic hydroborations and hydrosilylations of ketones and pyridines. We found that hydroborations of two ketones with pinacolborane using various Mg precatalysts is very rapid at room temperature with very low catalyst loadings, and ketone hydrosilylation using phenylsilane is rapid at 70 °C. Our studies point to an insertion/σ-bond metathesis catalytic cycle of an in situ formed "MgH2 " active species.

Stabilisation of carbonyl free amidinato-manganese(II) hydride complexes: "masked" sources of manganese(I) in organometallic synthesis.

Reaction of the amidinato-manganese(ii) bromide complex, [{(κ(2)-N,N'-Piso)Mn(µ-Br)}3(THF)2] (Piso = [(DipN)2CBu(t)](-), Dip = 2,6-diisopropylphenyl), with K[BHEt3] affords the first example of a structurally authenticated amidinato-manganese(ii) hydride complex, [{(N-,η(3)-arene-Piso)Mn(µ-H)2}2], via a process which involves a change in the amidinate coordination mode. Treatment of the bulkier precursor complex, [{(Piso'')Mn(µ-Br)}n] (Piso'' = [(Dip''N)2CBu(t)](-), Dip'' = C6H2Pr(i)2(CPh3)-2,6,4), with K[BHEt3] did not lead to an isolable manganese hydride complex, but its reaction with the magnesium(i) complex, [{((Mes)Nacnac)Mg}2] ((Mes)Nacnac = [(MesNCMe)2CH](-), Mes = mesityl), did. This reaction presumably proceeds via a reactive manganese(i) intermediate, which abstracts hydrogen from a reaction component to give [{(κ(2)-N,N'-Piso'')Mn(µ-H)}3]. A comparison of the reactivities of [{(N-,η(3)-arene-Piso)Mn(µ-H)2}2] and the isomorphous manganese(i) complex, [{(N-,η(3)-arene-Piso)Mn}2], toward CO, O2 and N2O was carried out. Reactions with the manganese(i) and manganese(ii) species gave identical results, namely the formation of the manganese(i) carbonyl complex, [(κ(2)-N,N'-Piso)Mn(CO)4] (reactions with CO), and the manganese(iii)-µ-oxo complex, [{(κ(2)-N,N'-Piso)Mn(µ-O)}2] (reactions with O2 and N2O). These results indicate that [{(N-,η(3)-arene-Piso)Mn(µ-H)2}2] can act as a "masked" source of an amidinato-manganese(i) fragment in synthetic transformations.

Neutral diiron(III) complexes with Fe2(µ-E)2 (E = O, S, Se) core structures: reactivity of an iron(I) dimer towards chalcogens.

Three neutral bis(µ-chalcogenido)diiron(III) complexes, [{(N,N'-Pipiso)Fe(µ-E)}2] (Pipiso(-) = [(DipN)2C(cis-2,6-Me2NC5H8)](-), (Dip = C6H3Pr(I)2-2,6; E = O, S or Se) have been prepared by reactions of the iron(I) dimer [{(µ-N,N'-Pipiso)Fe}2] with O2, S8 or Se∞. Treating the µ-selenido compound [{(N,N'-Pipiso)Fe(µ-Se)}2] with O2 cleanly generated its µ-oxo counterpart, [{(N,N'-Pipiso)Fe(µ-O)}2]. X-ray crystallographic analyses of the compounds showed them to possess Fe2(µ-E)2 core structures with distorted square planar (E = O) or tetrahedral (E = S or Se) iron coordination geometries. Magnetic, (57)Fe Mössbauer spectroscopic and computational studies indicate medium to strong antiferromagnetic coupling between the two high-spin Fe(III) ions in all three compounds.

Bulky guanidinato nickel(I) complexes: synthesis, characterization, isomerization, and reactivity studies.

Reactions of lithium complexes of the bulky guanidinates [{(Dip)N}(2)CNR(2)](-) (Dip=C(6)H(3)iPr(2)-2,6; R=C(6)H(11) (Giso(-)) or iPr (Priso(-)), with NiBr(2) have afforded the nickel(II) complexes [{Ni(L)(µ-Br)}(2)] (L=Giso(-) or Priso(-)), the latter of which was crystallographically characterized. Reduction of [{Ni(Priso)(µ-Br)}(2)] with elemental potassium in benzene or toluene afforded the diamagnetic species [{Ni(Priso)}(2)(µ-C(6)H(5)R)] (R=H or Me), which were shown, by X-ray crystallographic studies, to possess nonplanar bridging arene ligands that are partially reduced. A similar reduction of [{Ni(Priso)(µ-Br)}(2)] in cyclohexane yielded a mixture of the isomeric complexes [{Ni(µ-κ(1)-N-,η(2)-Dip-Priso)}(2)] and [{Ni(µ-κ(2)-N,N'-Priso)}(2)], both of which were structurally characterized. These complexes were also formed through arene elimination processes if [{Ni(Priso)}(2)(µ-C(6)H(5)R)] (R=H or Me) were dissolved in hexane. In that solvent, diamagnetic [{Ni(µ-κ(1)-N-,η(2)-Dip-Priso)}(2)] was found to slowly convert to paramagnetic [{Ni(µ-κ(2)-N,N'-Priso)}(2)], suggesting that the latter is the thermodynamic isomer. Computational analysis of a model of [{Ni(µ-κ(2)-N,N'-Priso)}(2)] showed it to have a Ni-Ni bond that has a multiconfigurational electronic structure. An analogous copper(I) complex [{Cu(µ-κ(2)-N,N'-Giso)}(2)] was prepared, structurally authenticated, and found, by a theoretical study, to have a negligible Cu···Cu bonding interaction. The reactivity of [{Ni(Priso)}(2)(µ-C(6)H(5)Me)] and [{Ni(µ-κ(2)-N,N'-Priso)}(2)] towards a range of small molecules was examined and this gave rise to diamagnetic complexes [{Ni(Priso)(µ-CO)}(2)] and [{Ni(Priso)(µ-N(3))}(2)]. Taken as a whole, this study highlights similarities between bulky guanidinate ligands and the ß-diketiminate ligand class, but shows the former to have greater coordinative flexibility.