Attempted 2-fold deprotonation of the bis(iminophosphorano)methane ligand, H(2)C(Ph(2)P=NSiMe(3))(2) (4-H(2)), with a calcium amide led only to mono-deprotonation. The crystal structure of (4-H)(2)Ca shows two tridentate ligands with short Ca-N and a rather long Ca-C bond. Reaction of 4-H(2) with a dibenzylcalcium complex gave the desired 2-fold deprotonation and formation of 4-Ca, which crystallized as a dimeric complex. Analysis of the calculated atomic and group charges in 4-H(2), (4-H)(2)Ca, and [4-Ca](2) showed that the negative charge at the imine nitrogens only slightly increases upon successive deprotonation of 4-H(2). The electron density at the central carbon, however, increases considerably: the charge on the carbene carbon in [4-Ca](2) is ca. -1.8. The negative charge in 4(2)(-) is therefore mainly located on the carbon. Reaction of [4-Ca](2) with benzophenone in benzene gave the remarkably stable adduct [4-Ca](2) x O=CPh(2), which was characterized by X-ray diffraction. Reaction of [4-Ca](2) with adamantylcyanide gave exclusive formation of the adduct [4-Ca](2) x (N identical withCR)(2), which did not react further, even at higher temperatures. Addition of cyclohexyl isocyanate to a benzene solution of [4-Ca](2) gave immediate [2 + 2]-cycloaddition and formation of a dianionic tetradentate ligand that binds to Ca(2+) through two nitrogens, the central carbon, and an oxygen. This product crystallized as a dimer with bridging oxygen atoms.

Twofold deprotonation of the bis-iminophosphorano ligand (DIPP-Nd(Ph 2 )P) 2 CH 2 (DIPP ) 2,6diisopropylphenyl) by (para-tBu-benzyl) 2 Ca‚(THF) 4 gave clean conversion to the monomeric THF adduct (DIPP-Nd(Ph 2 )P) 2 CCa‚(THF) 2 (2). This monomeric calcium carbene showed the same sluggish reactivity toward unsaturated electrophiles as the dimeric calcium carbene [(Me 3 Si-Nd(Ph 2 )P)CCa] 2 . No reaction was observed with 1-adamantyl cyanide, and with benzophenone a coordination complex was isolated: (DIPP-Nd(Ph 2 )P) 2 CCa‚(THF)‚(OdCPh 2 ) (4). Reaction with a slight excess of cyclohexyl isocyanate gave the double-insertion product(5). The monomeric calcium carbene 2 is a very slow catalyst for the trimerization of cyclohexyl isocyanate but a much faster catalyst for the trimerization of phenyl isocyanate. Crystal structures for 2, 4, and 5 are presented.

Size does matter: Whereas geminal bimetallic bis(amidophosphorano)methandiide complexes of the heavy alkali metals K and Rb are relatively stable, that of Cs, the largest and most electropositive of the alkali metals, decomposes to form a cyclic product, which cocrystallizes with benzylcesium.

Reaction of (Me 3 SiNdPPh 2 ) 2 CH 2 with Ba[N(SiMe 3 ) 2 ] 2 in 1:1 ratio gave only monodeprotonation and the homoleptic product [(Me 3 SiNdPPh 2 ) 2 CH] 2 Ba (3-Ba) was formed. Reaction with the strong base dibenzylbarium gave fast and clean 2-fold deprotonation and the dimeric complex [(Me 3 SiNdPPh 2 ) 2 -CBa‚THF] 2 (1-Ba) was isolated. Also the bulkier ligand (2,6-iPr 2 C 6 H 3 -NdPPh 2 ) 2 CH 2 was doubly deprotonated by this reagent, which gave clean formation of the monomeric complex (2,6-iPr 2 C 6 H 3 -NdPPh 2 ) 2 CBa‚(THF) 3 (2-Ba). Although organobarium compounds generally show high reactivity, the monomeric barium carbene complex 2-Ba reacted sluggishly with benzophenone or adamantyl cyanide and reaction products could not be identified. Reaction of 2-Ba with cyclohexyl isocyanate, however, cleanly gave the [2+2]-cycloaddition product, which crystallized as a dimer (4). Crystal structures of monomers 2-Ba and 3-Ba and dimers 1-Ba and 4 show in all cases tridentate (C, N, N′)-coordination of the bis-iminophosphorano ligand. In some cases the large coordination sphere of Ba 2+ was saturated by agostic iPr‚‚‚Ba 2+ and π-Ph‚‚‚Ba contacts.

Chloro[2,6-bis{1-(phenyl)iminoethyl}pyridine]rhodium(I) complexes (RhCl(N,N,N); 1-11) have been prepared by reaction of the dimer [Rh(μ-Cl)(η 2 -C 2 H 4 ) 2 ] 2 with the corresponding nitrogen donor ligand. These complexes afford nanoparticles with a mean diameter of 1.5 ( 0.2 nm stabilized by the partially hydrogenated ligand, under 1 atm of hydrogen, in 2-propanol as solvent, at 60°C, and in the presence of K t BuO. Under a constant atmospheric pressure of hydrogen, the nanoparticles catalyze the dehalogenation of the chlorobenzene 1,2-, 1,3-, and 1,4-dichlorobenzene, 1,2,4-trichloro benzene, fluorobenzene, 2-, 3-, and 4-chlorobiphenyl, and 4,4 0 -and 3,5-dichlorobiphenyl and the hydrogenation of benzene, toluene, p-xylene, styrene, R-methylstyrene, biphenyl, aniline, phenol, and pyridine. A Hg(0) poisoning test reveals that homogeneous and heterogeneous catalysis coexist during the dehalogenation reactions, whereas the hydrogenation processes are heterogeneous. The nanoparticles can be also generated in the presence of basic aluminum oxide of 150 mesh, which at the same time acts as a support. When they are deposited on the alumina, the nanoparticles do not significantly modify their catalytic activity.