for aid in obtaining the high field NMR, X-ray diffraction, and high-resolution mass spectral data, respectively. Supplementary Material Available: Spectroscopic and analytical data for (+)-2, (+)-3, (+)-7, (+)-8, (+)-ll, (+)-16, and (-)-17(2 pages). Ordering information is given on any current masthead page.

The hydrazine adducts (Me3C)3E<--NH2-N(H)-Me [E = Al (1), Ga (2)] afforded the corresponding dimeric hydrazides [(Me3C)2E-N(H)-N(H)-Me]2 (3 and 4) upon heating to 95 and 300 degrees C, respectively, by the release of isobutane. The molecular structure of 3 in the solid state comprises a five-membered Al2N3 heterocycle (3b), while 4 possesses a four-membered Ga2N2 ring with two exocyclic hydrazine groups (4a). Quantum-chemical calculations revealed only small energetic differences between both isomers. The structures determined in the solid state correspond to the thermodynamically favored ones. In solution, equilibrium mixtures between both forms were detected. Further thermolysis of the aluminum compound 3 gave different products depending on the reaction conditions. Below its melting point, isobutane was released. A cage compound (5) was formed, which has four Al-CMe3 groups and four hydrazindiido ligands [N(H)-N(Me)]2- with all N-N bonds enclosed in the cage. Fast heating of 3 above the melting point (149 degrees C) yielded a singular product (6) by a remarkable rearrangement process and formal release of ammonia. The hydrazonido ligand [N(Me)-N(=CH2)]- resulted, which has a reformed N-N bond and an N=C double bond and is in a bridging position between two aluminum atoms. An amido group (NH2) completes the five-membered Al2N3 heterocycle of 6.

Reaction of MesP─C≡C─Ph (Mes = mesityl) with dineopentylaluminium hydride afforded by hydroalumination a geminal Al/P-based frustrated Lewis pair (FLP; ). Its steric shielding is relatively low, and its reactivity in various secondary reactions is less hindered by steric repulsion than observed for related compounds having bulkier groups attached to aluminium. FLP yielded adducts with MeC─NCO or benzaldehyde via the formation of Al-O and P-C bonds. Trimethylsilyl azide reacted with under surprisingly mild conditions to afford a nitrene complex by spontaneous N elimination below room temperature. A carbodiimide molecule was coordinated via one of the C=N bonds to form a five-membered AlCPNC heterocycle with an intact C=N bond in an exocyclic position. A very large molecule was obtained by the reaction of two equivalents of with a bifunctional methylene-bridged phenylene isocyanate precursor.This article is part of the themed issue 'Frustrated Lewis pair chemistry'.

The P−H functionalized FLPs R(H)PC(AlBis 2 )C(H)-CMe 3 (1a, R = Bis; 1b, R = Mes; Bis = CH(SiMe 3 ) 2 ) combine the typical FLP properties based on Lewis acidic Al and basic P atoms with the reactivity of a P−H bond. They allow the coordination of substrates followed by hydrophosphination with the activated P−H group. Reactions of 1a with R′−NCS (R′ = Ph, CMe 3 ) or of both FLPs with Et−N CCPh 2 afforded five-membered AlCPCS/N heterocycles (4 and 5) via coordination of CS or CN bonds to the FLP backbone. Isomerization by a 1,3-H shift from P to N or C (6 and 7) was only achieved in the presence of an auxiliary base (DABCO; 1−5 mol %). (Z)-1a coordinated CO 2 to yield the adduct 8, which features a five-membered AlCPCO heterocycle with an exocyclic CO bond. Addition of bases such as DABCO and DBU afforded by deprotonation of the P atom the compounds [Bis-PC(AlBis 2 )C(H)−CMe 3 (CO 2 )] − [HB] + (9a, B = DABCO; 9b, B = DBU) that displayed hydrogen bonding between the ammonium ions and the exocyclic O atom of the FLP adducts in solution and the solid state. The stronger base n-BuLi afforded the dimeric Li compound 10, in which the Li cation was coordinated in a chelating manner to the oxygen atoms of one FLP adduct and additionally to the exocyclic O atom of the second adduct, resulting in a fourmembered Li 2 O 2 heterocycle. The related reaction of (Z)-1a with DABCO(SO 2 ) 2 led in contrast to the elimination of BisH and formation of a SO 2 -bridged dimer that features a central (AlOSO) 2 heterocycle with Al−O and S−O single bonds. The resulting unusual structural motifs may be derived from those of dialkylcarbamic or dialkylamidosulfinic acids with the N atoms replaced by P atoms.

A surprisingly easy access to the preparation of transition‐metal clusters is the reaction of MCl2 (M  Co, Ni) with PhP(SiMe3)2 and PPh3. In this way [Co4(μ3‐PPh)4(PPh3)4] and [Ni8(X)4(μ4‐PPh)6(PPh3)4] (XCl and CO) can be isolated. The paramagnetic complex with X  Cl contains 116 valence electrons and can be considered as a mixed‐valence cluster of Ni0 and Ni1+.