Phosphorus bridges

Many variants of complex (29) have been described, including hydrocarbyl bridged analogs117"-123 and amido fluorenyl complexes124 Examples of alkyl-substituted phosphorus bridges have also been reported. For example, complex (30) produces linear PE with an activity of lOOgmmol-1 h-1bar-1.125... 

Chiral bis-(binaphthophosphole) (bis(BNP)) ligands have been used in the asymmetric hydroformylation of styrene. In solution, the free diphospholes display fluxional behavior. Consistent with their structure, the reaction of the bis(BNP) compounds with platinum(II) derivatives gives either cis chelate mononuclear complexes or trans phosphorus-bridged polynuclear derivatives. Coordination to platinum enhances the conformational stability of bis(BNP)s and diastereomeric complexes can be detected in solution. In the presence of SnCl2, the platinum complexes give rise to catalysts that exhibit remarkable activity in the hydroformylation of styrene. Under optimum conditions, reaction takes place with high branched selectivity (80-85%) and moderate enantio-selectivity (up to 45% ee). 

The cavitands are essentially synthesized from their resorc[4]arene precursors which are readily obtained by resorcinol condensation with aldehydes. The main feature comes from the different configurations that are expected for this tetrameric species and the relative thermodynamical stability of each isomer, which has been widely investigated by several authors. In addition, the conformational mobility of the resorc[4]arene molecules will depend on substitution at the upper and lower rims [28, 36, 40, 41]. The first attempt to synthesize a phosphorus bridged cavitand was to treat resorc[4]arene la (1, R=CH3) with phenylphosphonic dichloride or phenylphosphonothioic dichloride. Only inseparable isomer mixtures were obtained and isolation of the desired cavitands was not possible [42]. The first isolated phosphorylated resorcinol-based cavitand was described in 1992 by Markovsky et al., who prepared compound D from la and four equivalents of o-phenylenechlorophos-phate in the presence of triethylamine [43, 44]. For this compound, a tautomeric temperature and solvent dependent equilibrium exists between the spirophosphorane structure and the cyclic phosphate form (Scheme 4). 

Phenyl phosphine and Fe(CO)5 at high temperatures form the open triangle of [25] (374), whereas the photolysis of Cp(CO)2Fe-PO(CF3)2 yields a phosphorus-bridged cluster Cp2Fe3(CO)2PO(CF3)2 of unknown structure (141, 142). Yet another cluster type [29] is formed from Fe(CO)5 and AsFg (135). 

In the absence of X-ray crystallographic data, 31P and 195Pt NMR spectroscopy is a useful method to investigate the nature of the products in the solution. In addition to earlier references to these topics, the Pople-Santry theory has been used to calculate the signs and relative magnitudes of the coupling constants for the type of phosphorus-bridged complexes covered in this section.1502... 

Nitrogen-phosphorus bridging ligands, in tetraosmium carbonyls, 6, 917... 

The ideas on the syntheses of di- and polynuclear complexes with phosphorus bridge by the method of direct (immediate) interaction of ligands and metal source can be received from the literature, summarized in Sec. 2.2.4.3, and related to the coordination compounds 239, 241, and 253. In this respect, we note that chelates can also participate as a metal source, for example in the transformation (3.68) [80] ... 

Another efficient class of chiral ligands, aryl diphosphites consisting of two or three BINOL units and two phosphorus bridges, was described by Chan et al. 8 Also, these ligands enabled Gu(OTf)2-catalyzed Michael additions of... 

The only example of Si H M agostic interaction supported by a phosphorus bridge was discovered by Driess et al. in the complexation of a silylated triphosphine ligand to a chromium tricarbonyl complex [Eq. (20)].143,144 A bigger metal (M = Mo) or smaller substituent at silicon (R = Ph) leads to the normal triphosphine complexes. The presence of a Si H "M interaction in 59 is deduced from the lack of C3 symmetry (evident from NMR), the red shift of the IR band for the coordinated Si-H bond (1994 cm-1 vs. 2142 cm-1), and the observation of a reduced Si-H coupling (135.7 Hz for the coordinated Si-H bond vs. 210.9 and 228.6 Hz for the free Si-H bonds). The X-ray structure determination of 59 shows that one of the phosphine ligands is tilted away from the chromium atom so that the... 

Sulphur- and phosphorus-bridged complexes of transition metals Lewis-base-metal carbonyl complexes... 

RING-OPENING POLYMERIZATION OF PHOSPHORUS-BRIDGED [1JFERROCENOPHANES... 

B. Synthesis, Properties, and Ring-Opening Polymerization of Phosphorus-Bridged [1 JFerrocenophanes... 

Examples of organometallic polymers containing both phosphorus atoms and transition metals in the backbone include polyferrocenylphosphines 8 (and the corresponding phosphine sulfides 9), which are accessible via the thermal ROP of phosphorus-bridged [1] ferrocenophanes [16,17]. Polymers of this type have been previously prepared by condensation routes and the catalytic potential of some of their transition metal derivatives has already been noted [18]. Living anionic ROP of phosphorus-bridged [l]ferrocenophanes has recently been demonstrated and provides a route to block copolymers such as 10 (PI = poly-isoprene) [19] ... 

Performing the reduction of the dichloride under an argon rather than dinitrogen atmosphere affords a phosphorus-bridged dizirconium complex where the bridging phenyl groups are reduced to bis(allyl) anions (341, Scheme 56).205 Addition of aryl alkynes to 338 offers another method of dinitrogen functionalization,... 

Phosphorus-bridged racemic salt metathesis route outlined in Scheme 278.917 The PhP-bridge has been extended to ansa-bis(Flu) zirconocene dichloride and ansa- Flu-Gp) zirconocene dichloride complexes. The pure rac-1186 was isolated, but a 1 2 rac/ meso-mixture of 1187 was obtained due to the inability to separate the two diastereomers by repeated recrystallization. Nevertheless, when activated with a large excess of MAO, the 1 2 rac/meso-mYxX.uxo of the 2,4-disubstituted // -zirconocene 1187 polymerizes liquid propylene at 50 °C to highly isotactic polypropylene with > 98%. 

High molecular-weight mixed-metal polyferrocenes have been prepared by Miyoshi et al. via the photochemical ROP of phosphorus-bridged [l]ferrocenophanes containing organometallic units on the phosphorus ligand (Scheme 2.14).111... 

Homo- and block copolymers from phosphorus-bridged [l]ferrocenophanes were isolated from living anionic ring opening polymerizations.113 Scheme 2.15 shows preparation of borane adducts of poly(ferrocenylphosphine)s by thermal ROP or addition of BX3 (X = H, Cl).114... 

Originally, Seyferth et al. reported the anionic ring-opening of phosphorus-bridged ferro-cenophanes in 1982.115 Subsequently, Manners reported the preparation of high molecular-weight... 

Finally, the main application of zirconium phosphanido complexes is to use them as metalloligands for coordination with the late transition metals to form phosphorus-bridged early-late heterobimetallic complexes. 

Although early attempts to induce the anionic ROP of phosphorus-bridged [I]ferrocenophanes only generated a mixture... 

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