Coordination Sphere of Transition Metals

Alkynes RC=CR may be t/ -bonded to transition metals M (XI). More often alkynes occupy a bridging position between two metal atoms, either perpendicular (Xlla) or parallel (Xllb) to the M—M bond (82). 

In the infant chemistry of iminoboranes only one example of insertion into a bridge position has been found [Eq. (56)] (86). That the structure of the product [Eq. (56)] corresponds to structure Xlla has been deduced from the CO absorption bands in the IR spectra, which 

The same iminoborane is thermally stabilized by cyclotrimerization, but may be cyclodimerized by the catalytic aid of /BuN=C (Section IB). The cyclodimer (BuBN Bu)2 produces the same product [Eq. (57b)] as for Eq. (57a). Nine further products of the same type, M[(R BNR)2], were prepared either from iminoboranes, from their cyclodimers, or from both the second starting component was either M(CO)5(OC4H8) (M = Cr, Mo, W), or Fe(CO)s or CpCo(C2H4)2, respectively (Table V). 

The structures of (OC)4Cr[(BuBNtBu)2] 49), (0C)4W[(BuBN/Bu)2] 89), and (OC)3Fe[(PrBNfBu)2] 89) were determined by X-ray methods. The diazadiboretidine ring skeleton is no longer planar the MB bonds 

The picture of the nitrogen atoms in diazadiboretidines acting as Lewis base centers is also supported by the formation of a 1 1 coordination compound with TiCl4 [Eq. (58)] (91). The B-NMR signal of 22.7 ppm indicates a highfield shift, which cannot be due to d-electrons from tetravalent d -titanium. X-Ray structural analysis shows that bridging chlorine atoms provide the observed electronic saturation of the boron atoms. 

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So, the active M—C bond in the propagation centers of heterogeneous catalysts is quite stable, its short lifetime being determined by its high kinetic lability as a result of the possibility of various reactions proceeding in the coordination sphere of transition metals. 

The coordination sphere of transition-metal complexes can furthermore be utilized for the fixation of silicon ligands in their lowest oxidation states. Even examples of compounds containing a formally zerovalent silicon (E) are now known [41]. 

Generation of Silylenes in the Coordination Sphere of Transition Metals... 

Compounds (L)AuC=CR can appear as ligands in the coordination sphere of transition metals. The interaction may be fluxional with metal-metal contacts M-Au and the alkyne coordinated side-on (if, dihapto) to the gold atom. Typical examples are (cp)(CO)(NO)W[Ph3PAuC=C Bu 90 and l, c3(CO)9[R3PAuC=CtBu], with R = Ph, Pr, for which several isomers have been observed in solution.91... 

Recently, Connick et al. (16a, b) have studied exchange reactions of water between the coordination sphere of transition metals and the solvent by O17 shifts. 

In spite of some declining industrial interest, the last 5 years have seen an unusual academic interest in the catalytic properties of the metal carbonyls. This has been part of a wider surge of interest in the organometallic chemistry of the transition metals and its application to homogeneous catalysis. Reactions such as Ziegler polymerization, the Oxo reaction, and the Wacker process are but a few of the many reactions of unsaturated molecules catalyzed in the coordination sphere of transition metal complexes (20). These coordination catalyses have much in common, and the study of one is often pertinent to the study of the others. 

P-Alkylation has also been shown to take place in the coordination sphere of transition metals affording the corresponding coordinated phospholium cations 112a and 112b in high yields <2001JOM131>. 

Oxazolin-2-ylidenes can also be used directly for coordination to metal atoms [109], but then they are not functionalised and therefore not covered by this book. However, it may be interesting to note that their generation is possible as a template synthesis in the coordination sphere of transition metal complexes using a functionalised hydroxyisocyanide [110,111] or the reaction of an epoxide with a hydrogen isocyanide complex [112]. 

P4, yield a variety of new compounds. Once in solution, higher condensed units such as Pi9, P2i, or P26" are accessible through metal-organic reactions, and they crystallize as solvates (for low coordinated phosphides stabilized in the coordination sphere of transition metals, see Scherer ). The species present in solvent-free and solvated phases usually differ. An example of the conversion of polyanions into alkylated polyphosphanes is P and PtRs. The latter can also be prepared from Na/K alloy and Pwhite in monoglyme with ClSiMes. Conversely, P7R3 is converted into solvated LisPy via metalation. Besides NH3(1), ethylenediamine, en, can be used for binding the alkah metal ions. 

Table 6 gives a survey on the range of M-P distances. The upper limits are uncertain because the selected distances are only compared with atomic radii and take not into account the topology (convex polyhedra procedure). The M-P coordination in sohd phosphides demonstrates both coordination and donor functions in isolated complex compounds (cf the (E15) complexes, stabihzed in the coordination sphere of transition metals). This is especially true with the polyphosphides. An extreme is CU2P3I2 (see Section 6.5.7), which is an adduct of Cul and elemental phosphorus (charge transfer complex). Chains of polycychc... 

Although no monomeric boranediyl species have yet been prepared, such ligands have been prepared in the coordination sphere of transition metals through the reaction of RBX2 with alkali metallates such as K2Fe(CO)4 Such an approach... 

ORGANOSELENIUM REACTANTS IN THE COORDINATION SPHERE OF TRANSITION METALS... 

The unstable thio, seleno-, and tellurofomialdehydes, CHjS, CHjSe, and CH2Te, can be trapped in the coordination sphere of transition metals... 

Mathey, F., Marinetti, A., Bauer, S., Le Floch, P. Chemistry of phosphorus-carbon double bonds in the coordination sphere of transition metals. Pure Appl. Chem. 1991, 63, 855-858. 

By design, ambiphilic ligands combine donor and acceptor sites on the same skeleton (Figure 1). The basic idea is to use donor sites as anchors to introduce Lewis acids in the coordination sphere of transition metals. Fine tuning of the structure of the ambiphilic ligands (coordination sites and linker) gives the possibility to control the position of the Lewis acid moiety and the way it participates in bonding and/or reactivity. 

In Ch. 21 Buntkowsky and Limbach review recent NMR work on the dynamics of dihydrogen and dideuterium in the coordination sphere of transition metals. In addition to inelastic neutron scattering and liquid state NMR, the effects of coherent (exchange couplings) and incoherent rotational tunneling of D2 pairs in transi-... 

The behavior of t-butylphosphaethyne in the coordination sphere of transition metals opens up an entirely new field of phosphorus compounds with unusual structures <88AG(E)1485, 88CRV1327>. 

The synthesis of tri-/-butyl-lP,32, 5A -triphosphinine arose from studies of the behavior of t-butylphosphaethyne (206) in the coordination sphere of transition metals. The first indication of the transition metal template catalyzed trimerization of (206) was the isolation of the vanadium-complexed 1,3,5-triphospha-Dewar benzene (207) <87AG(E)908>. The formation of the tetra-phosphabarrelene complexed to zirconium (208) implied the intermediate formation of the com-plexed tri-(-butyltriphosphinine derivative. The free barrelene could be obtained by oxidative decomplexation using C2CI6 <95AG(E)8i>. 

We will complete onr list of naked phosphorus units with P , P ", V - and Pj (see Fig. 7.41), all of which can be generated in the coordination sphere of transition metals, either by the elimination of subsituents on phosphorus, or by transfer of phosphorus units from one transition metal to the other. 

P4, yield a variety of new compounds. Once in solution, higher condensed units such as Pig , Pzi, or P26 are accessible through metal-organic reactions, and they crystallize as solvates (for low coordinated phosphides stabilized in the coordination sphere of transition metals, see Scherer ). 

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