ABSTRACT
A general synthetic strategy for the systematic synthesis of group 4 MIV heterometallic complexes LMIII(H)(µ-O)Si(µ-O)(OtBu)2}nMIV(NR2)4-n (L = {[HC{C(Me)N(2,6-iPr2C6H3)}2; MIII = Al or Ga; n = 1 or 2; MIV = Ti, Zr, Hf; R = Me, Et), based on alumo- or gallosilicate hydride ligands bearing a Si-OH moiety, is presented. The challenging isolation of these metalloligands involved two strategies. On the one hand, the acid-base reaction of LAlH2 with (HO)2Si(OtBu)2 yielded LAlH(µ-O)Si(OH)(OtBu)2 (1), while on the other hand, the oxidative addition of (HO)2Si(OtBu)2 to LGa produced the gallium analog (2). These metalloligands successfully stabilized two hydrogen atoms with different acid-base properties (MIII-H and SiO-H) in the same molecule. Reactivity studies between 1 and 2 and group 4 amides MIV(NR2)4 (MIV = Ti, Zr, Hf; R = Me, Et) and tuning the reactions conditions and stoichiometry led to isolation and structural characterization of heterometallic complexes 3-11 with a 1:1 or 2:1 metalloligand/MIV ratio. Notably, some of these molecular heterometallic silicate complexes stabilize for the first time terminal (O3Si-O-)MIV(NR2)3 moieties known from single-site silica-grafted species. Furthermore, the aluminum-containing heterometallic complexes possess Al-H vibrational energies similar to those reported for modified alumina surfaces, which makes them potentially suitable models for the proposed MIV species grafted onto silica/alumina surfaces with hydride and dihydride architectures.
ABSTRACT
The heterobimetallic complexes [Co(LtzE)3K(THF)2] [LtzE = [{4,5-(P(E)Ph2)2}tz]-; tz = 1,2,3-triazole; E = S(3), Se(4)] featuring high-spin cobalt centres, and [Ni(LtzE)3K(THF)2] [E = S(5), Se(6)] were synthesized through the self-assembly reaction of HLtzE [E = S(1), Se(2)], KOH or K0 and MCl2 (M = Co, Ni). Compounds 3-6 exhibit an unusual metallascorpionate-type anion formed by the coordination of three triazole units via a κ2-N,E mode to the transition-metal atom, and this anion further coordinates to a potassium cation through a κ3-N',N'',N''' fashion. Compounds 3 and 5 were used in the synthesis of 3d-metal heterometallascorpionates [M(LtzS)3Cu(PPh3)] [M = Co, (7), M = Ni (8)] and the bimetallic complex [Ni(LtzE)3Ni(NO3)(THF)] (9) through metathesis reactions, pointing to stable metallascorpionate anions in solution. The solution behavior of 3-9 was investigated by UV-visible spectroscopy, high-resolution mass spectrometry, electrochemical methods and by magnetic-susceptibility measurements. The molecular structures of 3-6, 8 and 9 were determined by single-crystal X-ray diffraction studies and exhibit MM' distances ranging from 3.52 to 3.88 Å.
ABSTRACT
The reaction of metalloxanes [{MeLM(OH)}2(µ-O)] [M = Al (1), Ga (2); MeL = CH{CMe(NAr)}2-, Ar = 2,4,6-Me3C6H2, Me = methyl] with an excess of BH3·D (D = tetrahydrofuran (THF), SMe2) affords annular metallaborate systems achieved through M-O-M cleavage. Compound 1 led exclusively to the formation of eight-membered ring systems [{MeLAl(µ-O){B(OnBu)}(µ-O)}2] (3) and [{MeLAl(µ-O)(BH)(µ-O)}2] (6), while for 2 the unprecedented six-membered ring systems [{(MeLGa)2(µ-O)}(µ-O)2{B(OnBu)}] (4) and [(MeLGa)(µ-O)2{(BOnBu)2(µ-O)}] (5) were observed. The use of BH3·THF with 1 and 2 led to the concomitant THF ring-opening reaction, while with BH3·SMe2 in THF no such reaction was observed. The metallaborates [MeLAl{OB(pinacol)}(OH)] (7) and [{MeLGa(OB(pinacol))}2(µ-O)] (8) were synthesized from pinacolborane and the corresponding metalloxane, providing structural evidence that supports the reaction pathways proposed for the formation of 3-6. Density functional theory studies were performed on 3-5 to assess the effect of the metal exchange between aluminum and gallium atoms on the energy of the general ring structures.
ABSTRACT
Controlled hydrolysis of (Me)LGaCl2 ((Me)L = HC[(CMe)N(2,4,6-Me3C6H2)]2(-)) (1) in the presence of a N-heterocyclic carbene, as a HCl acceptor, led to the unprecedented molecular galloxane dihydroxide [{(Me)LGa(OH)}2(µ-O)] (2) in high yield. Compound 2 was used in the assembly of the heterobimetallic galloxanes with group 4 metals [{((Me)LGa)2(µ-O)}(µ-O)2{M(NR2)2}] (M = Ti, R = Me (6); M = Zr (7), Hf (8), R = Et).
