A series of β-diketiminate stabilized aluminium hydrides of the type (Nacnac)Al(R)H has been synthesized offering variation in the auxiliary R substituent and in the Nacnac backbone. These show significant variation in the nature of the Al-H bond: electron-donating R groups give rise to weaker (and presumably more hydridic) Al-H bonds, leading to enhanced rates of reactivity towards CO . The resulting κ -formate complexes (Nacnac)Al(R){OC(O)H} have been isolated and their reactivity towards B-H-containing reductants probed. In the case of HBpin no reaction is observed (even under forcing conditions), while the more reactive boranes HBcat and {H(9-BBN)} ultimately yield boryloxy complexes of the type (Nacnac)Al(R)(OBX ) (X =cat, 9-BBN). However, no hint of Al-O/B-H metathesis is observed even under forcing conditions. With BH ⋅SMe the major product is a related boryloxy system, although (uniquely) in this case a minor product is observed which contains an Al-H bond. We hypothesize that (Nacnac)Al(R)(κ -BH ) is formed (despite the unfavourable thermodynamics of Al-O/B-H metathesis) due to the additional driving force provided by coordination of the strongly Lewis acidic BH unit to the Al-H bond. That said, we find that (unlike the analogous gallium systems) no catalytic turnover can be achieved in the reduction of CO by boranes mediated by these aluminium hydrides.

Bond activation at a transition metal centre is a key fundamental step in numerous chemical transformations. The oxidative addition of element-hydrogen bonds, for example, represents a critical step in a range of widely applied catalytic processes. Despite this, experimental studies defining steps along the bond activation pathway are very rare. In this work, we report on fundamental studies defining a new oxidative activation pathway: combined experimental and computational approaches yield structural snapshots of the simultaneous activation of both bonds of a β-diketiminate-stabilized GaH unit at a single metal centre. Systematic variation of the supporting phosphine ligands and single crystal X-ray/neutron diffraction are exploited in tandem to allow structural visualization of the activation process, from a η-H,H σ-complex showing little Ga-H bond activation, through species of intermediate geometry featuring stretched Ga-H and compressed M-H/M-Ga bonds, to a fully activated metal dihydride featuring a neutral (carbene-type) N-heterocyclic Ga ligand.

We present anovel approach for constructing chains of Group 14 metal atoms linked by unsupported metal-metal bonds that exploits hemilabile ligands to generate unsaturated metal sites.T he formation/nature of catenated species (oligodimetallynes) can be controlled by the use of (acidic/basic) "protecting groups" and through variation of the ligand scaffold.Reduction of Ar NiPr2 GeCl (Ar NiPr2 = 2,6-( i Pr 2 NCH 2 ) 2 C 6 H 3 )-featuring hemilabile N i Pr 2 donors-yields (Ar NiPr2 Ge) 4 (2), which contains at etrameric Ge 4 chain. 2 represents an ovel type of al inear homo-catenated Ge I compound featuring unsupported E À Eb onds.T rapping experiments reveal that ak ey structural component is the central two-way Ge = Ge donor-acceptor bond:r eactions with IMe 4 and W(CO) 5 (NMe 3 )g ive the base-or acid-stabilized digermynes (Ar NiPr2 Ge(IMe 4 )) 2 ( 4)and (Ar NiPr2 Ge{W(CO) 5 }) 2 (5), respectively.The use of smaller N-donors leads to stronger Ge-N interactions and quenchingo fc atenation behaviour: reduction of Ar NEt2 GeCl gives the digermyne (Ar NEt2 Ge) 2 , while the unsymmetrical system Ar NEt2 GeGeAr NiPr2 dimerizes to give tetranuclear (Ar NEt2 GeGeAr NiPr2 ) 2 through aggregation at the N i Pr 2 -ligated Ge I centres.

A novel β‐diketiminate stabilized gallium hydride, (DippL)Ga(Ad)H (where (DippL)={HC(MeCDippN)2}, Dipp=2,6‐diisopropylphenyl and Ad=1‐adamantyl), has been synthesized and shown to undergo insertion of carbon dioxide into the Ga−H bond under mild conditions. In this case, treatment of the resulting κ1‐formate complex with triethylsilane does not lead to regeneration of the hydride precursor. However, when combined with B(C6F5)3, (DippL)Ga(Ad)H catalyses the reductive hydrosilylation of CO2. Under stoichiometric conditions, the addition of one equivalent of B(C6F5)3 to (DippL)Ga(Ad)H leads to the formation of a 3‐coordinate cationic gallane complex, partnered with a hydroborate anion, [(DippL)Ga(Ad)][HB(C6F5)3]. This complex rapidly hydrometallates carbon dioxide and catalyses the selective reduction of CO2 to the formaldehyde oxidation level at 60 °C in the presence of Et3SiH (yielding H2C(OSiEt3)2). When catalysis is undertaken in the presence of excess B(C6F5)3, appreciable enhancement of activity is observed, with a corresponding reduction in selectivity: the product distribution includes H2C(OSiEt3)2, CH4 and O(SiEt3)2. While this system represents proof‐of‐concept in CO2 hydrosilylation by a gallium hydride system, the TOF values obtained are relatively modest (max. 10 h−1). This is attributed to the strength of binding of the formatoborate anion to the gallium centre in the catalytic intermediate (DippL)Ga(Ad){OC(H)OB(C6F5)3}, and the correspondingly slow rate of the turnover‐limiting hydrosilylation step. In turn, this strength of binding can be related to the relatively high Lewis acidity measured for the [(DippL)Ga(Ad)]+ cation (AN=69.8).

We report on the synthesis of adistannyne supported by ap incer ligand bearing pendant amine donors that is capable of reversibly activating E-H bonds at one or both of the tin centres through dissociation of the hemi-labile N-Sn donor/acceptor interactions.This chemistry can be exploited to sequentially (and reversibly) assemble mixed-valence chains of tin atoms of the type ArSn{Sn(Ar)H} n SnAr (n = 1, 2). The experimentally observed (decreasing) propensity towards chain growth with increasing chain length can be rationalized both thermodynamically and kinetically by the electronwithdrawing properties of the -Sn(Ar)H-backbone units generated via oxidative addition.

Reactions of the β-diketiminate-stabilized gallium dihydride (Nacnac) GaH with chelating Ir bis(phosphine) precursors under an H atmosphere are shown to provide a simple route to Ir complexes stabilized by strongly σ-donating hydrides and the carbene-like (Nacnac) Ga donor. Characterization of these systems as seven-coordinate Ir tetrahydride species is supported by single crystal X-ray and neutron diffraction, and by T NMR measurements. By contrast related systems featuring more sterically demanding (non-chelating) ancillary ligands are better described in terms of a bis(hydride) dihydrogen [L Ir(H) (H )] formulation and a formal Ir oxidation state.

Aluminium borohydrides of the type (Nacnac)Al(R){H2(9-BBN)} are characterized by borane dissociation in solution under ambient conditions. This behaviour is critical to the ability of such complexes to reduce CO2.

We report on the reversible uptake of carbon dioxide by dimetallynes featuring ancillary hemi-labile pincer ligands. Insertion into the GeÀ Ge/SnÀ Sn bonds yields species containing an E(CO 2 )E unit, with the mode of ligation of the CO 2 fragment determined crystallographically being found to be dependent on the identity of the Group 14 element. The thermodynamics of CO 2 uptake/loss can be established through VT NMR (ΔH°= + 24.6(2.3) kJ mol À 1 , ΔS°= + 64.9(3.8) J mol À 1 K À 1 , ΔG°2 98 = + 5.3(1.9) kJ mol À 1 for the loss of CO 2 in the Ge case), and the chemical consequences of reversibility demonstrated by thermodynamically-controlled exchange reactions.