The reaction of a solution of B(C6F4H)3 and either iPr3P or tBu3P with CO2 afforded the species R3P(CO2)B(C6F4H)3 (R=iPr (1), tBu (2)). In a similar fashion the boranes, RB(C6F5)2 (R=hexyl, cyclohexyl (Cy), norbornyl), ClB(C6F5)2, or PhB(C6F5)2 were combined with tBu3P and CO2 to give the species tBu3P(CO2)BR(C6F5)2 (R=hexyl (3), Cy (4), norbornyl (5), Cl (6), Ph (7)). Similarly, the compounds [tBu3PH][RBH(C6F5)2] (R= hexyl (8), Cy (9), norbornyl (10)) were prepared by reaction of the precursor frustrated Lewis pair (FLP) with H2. Subsequent reactions of 9 and 10 with CO2 afforded the species [((C6F5)2BR)2(μ-HCO2)][tBu3PH] (R= Cy (11), norbornyl (12)). In related chemistry, combinations of the boranes RBG(C6F5)2 (R=hexyl, Cy, norbornyl) with tBu3P treated with an equivalent of formic acid gave [(C6F5)2BR(HCO2)][tBu3PH] (R=hexyl (13), Cy (14), norbornyl (15)). Subsequent addition of an additional equivalent of borane provides a second synthetic route to 11 and 12. Crystallographic studies of compounds 2-6 and 8-14 are reported and discussed. Further understanding of the FLP complexation and activation of CO2 is provided by computational studies.

Aluminum−phosphorus-based frustrated Lewis pairs (Al/P FLPs) are valuable reagents for the dipolar activation or coordination of small molecules or ionic compounds. They are accessible by hydroalumination of alkynylphosphines. However, as reported in this article, the application of this simple method for the synthesis of a broad variety of different compounds is limited to sterically shielded systems. Hydroalumination of Mes 2 PCCPh with small dialkyl-or diarylaluminum hydrides HAlR 2 (R = Me, iBu, Ph) afforded unique adducts in which an HAlR 2 molecule was coordinated by the Al/P FLP Mes 2 PC(CHPh)AlR 2 via an Al−P and an Al−H−Al 3c bond. A new Al/P FLP was obtained with equimolar quantities of dineopentylaluminum hydride. The less shielded alkynylphosphine Ph 2 PCCPh yielded a hydride adduct with HAlNp 2 and an alkyne adduct with HAltBu 2 . The latter compound resulted from triple-bond activation and had a five-membered AlPC 3 heterocycle in which a CC bond was bonded to the P and Al atoms of an Al/P FLP. Both compounds were isolated in high yields by application of the appropriate stoichiometric ratios of the starting materials.

Treatment of the alkynyl(diethylamino)germanes Et 2 NGe(CC t Bu) 3 ( 1) and (Et 2 N) 2 Ge(CC t Bu) 2 (2) with dialkylelement hydrides t Bu 2 MH (M = Al, Ga) afforded in high yields the hydrometalation products). The Lewis acidic aluminum and gallium atoms showed a close contact to the nitrogen atoms of the amino groups attached to germanium, which resulted in relatively long Ge−N bonds and short Al−N or Ga−N distances. The structures of these molecules and the strengths of the interactions were investigated by dispersion-corrected density functional theory. This activation of the Ge−N bonds caused an unprecedented reactivity of compounds 4b and 6. 4b reacted with PhCCH under mild conditions and elimination of HNEt 2 to give the mixed dialkynyl compound ( t BuCC)(PhCC)Ge[C(Ga t Bu 2 )C(H) t Bu] 2 (5), while facile insertion of RNCX into a Ge−N bond of 6 led to the formation of the six-membered Ge−C−Ga−X−C−N heterocycles 7 (R = Ph, Et; X = O, S).

Treatment of various diethynylgermanes, (R1)2Ge(C≡C–R2)2 (R1 = C6H5, CH3; R1–R1 = C6H4–C6H4; R2 = CH3, CMe3, nBu, C6H5), with equimolar quantities of di(tert‐butyl)aluminium or ‐gallium hydride, R2E–H (E = Al, Ga), afforded mixed alkenyl‐alkynylgermanes, (R1)2Ge(C≡C–R2)[C{E(CMe3)2}=C(H)–R2], by reduction of one of their C≡C triple bonds. The alkenyl groups have a cis arrangement of H and Al or Ga atoms across the C=C double bonds, which reflects the kinetically favoured situation. The cis/trans isomerisation is probably prevented from yielding thermodynamically favoured trans isomers; this is a result of an intramolecular bonding interaction between the α‐carbon atoms of the remaining ethynyl groups and the coordinatively unsaturated metal atoms. The higher Lewis acidity of Al compared to Ga results in relatively short Al···C(ethynyl) contacts (>231.2 pm) and a concomitant lengthening of the Ge–C bonds.

Hydrometallation of iPr2 N-Ge(CMe3 )(C≡C-CMe3 )2 with H-M(CMe3 )2 (M=Al, Ga) affords alkenyl-alkynylgermanes in which the Lewis-acidic metal atoms are not coordinated by the amino N atoms but by the α-C atoms of the ethynyl groups. These interactions result in a lengthening of the Ge-C bonds by approximately 10 pm and a comparably strong deviation of the Ge-CC angle from linearity (154.3(1)°). This unusual behaviour may be caused by steric shielding of the N atoms. Coordination of the metal atoms by the amino groups is observed upon hydrometallation of Et2 N-Ge(C6 H5 )(C≡C-CMe3 )2 , bearing a smaller NR2 group. Strong M-N interactions lead to a lengthening of the Ge-N bonds by 10 to 15 pm and a strong deviation of the M atoms from the MC3 plane by 52 and 47 pm, for Al and Ga, respectively. Dual hydrometallation is achieved only with HAl(CMe3 )2 . In the product, there is a strong Al-N bond with converging Al-N and Ge-N distances (208 vs. 200 pm) and an interaction of the second Al atom to the phenyl group. Addition of chloride anions terminates the latter interaction while the activated Ge-N bond undergoes an unprecedented elimination of EtN=C(H)Me at room temperature, leading to a germane with a Ge-H bond. State-of-the-art DFT calculations reveal that the unique mechanism comprises the transfer of the amino group from Ge to Al to yield an intermediate germyl cation as a strong Lewis acid, which induces β-hydride elimination, with chloride binding being crucial for providing the thermodynamic driving force.