Calcium Carbene complexes

Despite the observation that phenyl- and 1-adamantylisocyanate may be used as substrates for hydroamination catalysis without polymerization or oligomerization of the unsaturated molecule (see Sect. 2.1.4), in the presence of catalytic quantities of a calcium carbene complex [ (ArN=PPh2)2C)Ca(THF)2] phenyl- and cyclohexylisocyanate have been reported to undergo a selective cyclotrimerization to form the corresponding isocyanurate (Scheme 24) [106, 146], Reactirms proceed at low temperature and with phenylisocyanate requiring a lower catalyst loading and shorter reaction time to reach higher conversion than cyclohexylisocyanate. 

It is also possible to isolate bis(carbene) complexes involving the heavier alkaline earth metals. Thus, the reaction of two equivalents of 4 (R = Me or (Bu, R = H) with calcium, strontium and barium bis(trimethylsilyl)amides [M N(SiMe3)2 2(thf)2] (M = Ca, Sr, Ba) resulted in the displacement of two thf molecules to afford the corresponding biscarbene species, 19 (19). The solubilities and stabilities of these complexes were found to decrease from calcium to barium. 

Benzenes and alkylbenzenes By ring forming reactions Calcium acetate, 60 Chromium carbene complexes, 82 Dicarbonylcyclopentadienylcobalt, 96... 

By ring forming reactions /rans-Bromotetracarbonyl(methyl-methylidyne)tungsten, 49 Calcium acetate, 60 Chromium carbene complexes, 82 Ethyl (Z)-3-bromoacrylate, 130 Methyllithium, 188 By ether cleavage Diphosphorus tetraiodide, 127 Other methods... 

Carbene complexes of alkaline earth metal amides and metallocenes have also been reported. Reaction of calcium, strontium, and barium bis(trimethylsilyl)amides [M(N(SiMe3)2 2(thf)2] (M = Ca, Sr, Ba) with two equivalents... 

Base for C-H or N-H Deprotonation of Precursors to Carbene or Amide Ligands in the Preparation of Metal Complexes. KHMDS has been used as a base for the deprotonation of N-H or B-H bonds in imine-based ligands or trispyrazolyl borate-derived ligands to synthesize calcium complexes, which were used as initiators of the ring-opening polymerization of lactides. A first example of a two-coordinate, neutral In singlet carbene complex has been prepared via an in situ deprotonation of the imine ligand precursor with KHMDS in the presence of In I to afford the In(I) complex in 36% unoptimized yield as pale yellow, thermally stable crystals. ... 

The monodeprotonation of the bis(iminophosphorano)methane (28), analogous to (7), with calcium bis(trimethylsilyl)amide led to complex (29), characterized by X-ray diffraction, while the 2-fold deprotonation using the dibenzylcalcium complex [Ca(CH2C6H4Bu )2(THF)4] gave the stabilized calcium carbene derivative that... 

The metal-donor bonds are predominantly ionic and become more labile for calcium, strontium, and barium compared to beryllium and magnesium. The solubility and stability of the complexes decrease from calcium to barium. The 1 1 adducts of NHCs with BH3 or BF3 (28 and 29) are thermally stable and can be sublimed without decomposition. This is in sharp contrast to the properties of conventional carbenes, which rely on a pronounced metal-to-ligand back donation and are, thus, not suited to forming adducts with electron-poor fragments such as... 

Dibenzyl complexes with calcium, strontium, barium, 2, 120 with Ti(IV), 4, 343, 4, 349 with Zr(IV), 4, 783, 4, 785-786 with Zr(IV) mono-Cp complexes, 4, 833 Dibenzylgallium azides, for semiconductor growth, 12, 17 Dibenzyl imido complexes, with Ti(IV), 4, 352-353 Dibenzyl phosphoranimino carbenes, with Zr(IV), 4, 798 Dibenzyl titanasilsesquioxanes, synthesis, 4, 493 Dibenzyo-tetramethyltetraaza[14]-annulenes, with Zr(IV),... 

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