B-H Functionalization of Hydrogen-Rich [(Cp*V)(2) (B2H6)(2)]: Synthesis and Structures of [(Cp*V)(2)(B2X2)(2)H-8] (X = CI, SePh; Cp* = eta(5)-C5Me5)

International audienceWe have recently reported the perchlorinated diniobaborane species [(Cp*Nb)(2)(B2H4Cl2)(2)] from [(Cp*Nb)(2)(B2H6)(2)] using CCl4 as a chlorinating agent. In an attempt to isolate the vanadium analogue, we have isolated [(Cp*V)(2)(B2H6)(2)] (1) from the reaction of (Cp*VCl2)(3) with [LiBH4THF] followed by thermolysis with excess [BH3 center dot THF]. Subsequently, the thermolysis of 1 with CCl4 for a prolonged period of time afforded the perchlorinated divanadaborane [(Cp*V)(2)(B2H4Cl2)(2)] (2) along with the formation of the bichlorinated divanadaborane [(Cp*V)(2)(B2H5Cl)(2)] (3) and trichlorinated divanadaborane [(Cp*V)(2)(B2H4Cl2)(B2H5Cl)] (4). Similarly, in order to functionalize the terminal B-H by a {SePh} group, thermolysis of 1 was carried out with Ph2Se2, which yielded the persubstituted divanadaborane [(Cp*V)(2) {B2H4(SePh)(2)}(2)] (5) in parallel to the formation of [(Cp*V)(2) {B4H11(SePh)}] (6). Compound 5 is very fascinating in that all of the terminal B-H hydrogens of 1 have been substituted by {SePh} ligands. All of the compounds have been characterized by H-1, B-11, and C-13 NMR spectroscopy, mass spectrometry, IR spectroscopy, and single-crystal X-ray analysis. Density functional theory (DFT) and TD-DFT calculations provided a further understanding regarding the electronic structures, bonding, and electronic transitions of these persubstituted vanadaborane species

Heterometallic Triply-Bridging Bis-Borylene Complexes

International audienceTriply-bridging bis-{hydrido(borylene)} and bis-borylene species of groups 6, 8 and 9 transition metals are reported. Mild thermolysis of [Fe-2(CO)(9)] with an in situ produced intermediate, generated from the low-temperature reaction of [Cp*WCl4] (Cp*=eta(5)-C5Me5) and [LiBH4.THF] afforded triply-bridging bis-{hydrido(borylene)}, [(mu(3)-BH)(2)H-2{Cp*W(CO)(2)}(2){Fe(CO)(2)}] (1) and bis-borylene, [(mu(3)-BH)(2){Cp*W(CO)(2)}(2){Fe(CO)(3)}] (2). The chemical bonding analyses of 1 show that the B-H interactions in bis-{hydrido (borylene)} species is stronger as compared to the M-H ones. Frontier molecular orbital analysis shows a significantly larger energy gap between the HOMO-LUMO for 2 as compared to 1. In an attempt to synthesize the ruthenium analogue of 1, a similar reaction has been performed with [Ru-3(CO)(12)]. Although we failed to get the bis-{hydrido(borylene)} species, the reaction afforded triply-bridging bis-borylene species [(mu(3)-BH)(2){WCp*(CO)(2)}(2){Ru(CO)(3)}] (2 '), an analogue of 2. In search for the isolation of bridging bis-borylene species of Rh, we have treated [Co-2(CO)(8)] with nido-[(RhCp*)(2)(B3H7)], which afforded triply-bridging bis-borylene species [(mu(3)-BH)(2)(RhCp*)(2)Co-2(CO)(4)(mu-CO)] (3). All the compounds have been characterized by means of single-crystal X-ray diffraction study; H-1, B-11, C-13 NMR spectroscopy; IR spectroscopy and mass spectrometry

Syntheses and structures of chalcogen-bridged binuclear group 5 and 6 metal complexes

International audienceSyntheses and structural elucidations of a series of chalcogen stabilized binuclear complexes of group 5 and 6 transition metals have been described. Room temperature reaction of [Cp*CrCl](2) (Cp* = eta(5)-C5Me5) with Li[BH3(SePh)] afforded a Se inserted binuclear chromium complex, [(Cp*Cr)(2)(mu-Se2SePh)(2)], 1. In an attempt to make the analogous complexes with heavier group 6 metals, reactions of [Cp*MCl4] (M = Mo and W) with Li[BH3(SePh)] were carried out that yielded Se inserted binuclear complexes [(Cp*M)(2)(mu-Se)(2)(mu-SePh)(2)], 2 and 3 (2 M = Mo and 3 M = W) along with known [(Cp*M)(2)B5H9], 4a-b (4a M = Mo and 4b M = W). Similarly, the reactions of [Cp*NbCl4] with Li[BH3(EPh)] (E = S or Se) followed by thermolysis led to the formation of binuclear chalcogen complexes [(Cp*Nb)(2)(mu-E-2)(2)], 5 and 6 (5 E = S and 6 E = Se) and known [(Cp*Nb)(2)(B2H6)(2)], 7. All these complexes have been characterized by H-1 and C-13 NMR spectroscopy and mass spectrometry. The structural integrity of complexes 1, 3, 5 and 6 was established by the X-ray diffraction studies. The DFT studies further exemplify the bonding interactions present in these complexes, especially the multiple bond character between the metals in 1-3

Synthesis, Structure and Chemistry of Mono- and Digallane Complexes Supported by N,O-Ketimine Ligand

International audienceA series of N,O-ketimine supported gallium and digallane complexes have been synthesized and structurally characterized. The mono(ketiminate) gallium dichloride [OCMeCHCMeN(Dipp)]GaCl2, 2 (Dipp=2,6-(Pr2C6H3)-Pr-i) and bis(ketiminate) gallium chloride [OCMeCHCMeN(Dipp)](2)GaCl, 3 were isolated from the reaction of GaCl3 with 1 and 2 equivalents of lithiated ketimine, [OCMeCHCMeN(Dipp)]Li, 1 respectively. Treatment of 1 with "GaI'' yielded diiodobis(ketiminate) digallane complex [OCMeCHCMeN-(Dipp)](2)Ga2I2, 4. To the best of our knowledge, compound 4 is the first report on N,O-ketiminate ligand supported stable heteroleptic digallane(II) complex. The frontier molecular orbital analysis and a high Wiberg Bond Index (WBI) values support the strong interaction between the gallium centers in 4. In an attempt to synthesize alkyl substituted Ga complexes, we carried out the reaction of ketimine ligand with (GaBu2Cl)-Bu-t (1:1 ratio) that generated the adduct [OCMeCHCMeN(H)(Dipp)](GaBu2Cl)-Bu-t, 5. In a similar fashion, dialkyl gallium complex [OCMeCHCMeN(Dipp)](GaBu2)-Bu-t, 6 was obtained from the reaction of 1 with (GaBu2Cl)-Bu-t. All the compounds have been charecterized by H-1, (CNMR)-C-13 and mass spectroscopy. The molecular structures of complexes 2-5 have also been determined by single crystal X-ray diffraction analysis

CO₂/Epoxide Coupling and the ROP of ε‑Caprolactone: Mg and Al Complexes of γ‑Phosphino-ketiminates as Dual-Purpose Catalysts

γ-Phosphino-ketimines Ph₂PC­[C­(Me)­O]­[C­(Me)­NAr] (Ar = 2,6-diisopropylphenyl, <b>L</b>^<b>1</b>H; Ar = 2,6-difluorophenyl, <b>L</b>^<b>2</b>H) were synthesized by treating deprotonated ketimines with PPh₂Cl. Their Mg complexes [(<b>L</b>^<b>1</b>)₂(THF)­Mg] (<b>1</b>) and [(<b>L</b>^<b>2</b>)₂(THF)₂Mg] (<b>2</b>) were obtained in excellent yields from a reaction between <b>L</b>H and di-<i>n</i>-butylmagnesium in THF. Addition of a slight excess of trimethylaluminum to <b>L</b>H in toluene yielded the Al complexes [<b>L</b>^<b>1</b>AlMe₂] (<b>3</b>) and [<b>L</b>^<b>2</b>AlMe₂] (<b>4</b>). Complexes <b>1</b> and <b>3</b> displayed high catalytic activity in the synthesis of cyclic carbonates from CO₂ and epoxides and also in the ring-opening polymerization (ROP) of ε-caprolactone. However, complexes <b>2</b> and <b>4</b>, which contain fluoro substituents, showed poor activity in the synthesis of cyclic carbonates and could not initiate the ROP reaction. The pentacoordinated Mg complex <b>1</b> was found to be a better catalyst than the aluminum complex <b>3</b>. It was also observed that the complexes <b>1</b> and <b>3</b> were more efficient than the unsubstituted ketiminate complexes reported in the literature

Stabilization of Classical B2H5](-): Structure and Bonding of (Cp*Ta)(2)(B2H5)(mu-H)L-2] (Cp*=eta(5)-C5Me5; L=SCH2S)

The room-temperature reaction of Cp*TaCl4] with LiBH4.THF followed by addition of S2CPPh3 results in pentahydridodiborate species (Cp*Ta)(2)(mu,eta(2):eta(2)-B2H5)(mu-H)(kappa(2),mu-S2CH2)(2)] (1), a classical B2H5](-) ion stabilized by the binuclear tantalum template. Theoretical studies and bonding analysis established that the unusual stability of B2H5](-) in 1 is mainly due to the stabilization of sp(2)-B center by electron donation from tantalum. Reactions to replace the hydrogens attached to the diborane moiety in 1 with a 2 e {M(CO)(4)} fragment (M=Mo or W) resulted in simple adducts, {(Cp*Ta)(CH2S2)}(2)(B2H5)(H){M(CO)(3)}] (6: M=Mo and 7: M=W), that retained the diborane(5) unit