Neutral phosphine

It was recently found that the modification of neutral phosphine ligands with cationic phenylguanidinium groups represents a very powerful tool with which to immobilize Rh-complexes in ionic liquids such as [BMIM][PFg] [76]. The guani-dinium-modified triphenylphosphine ligand was prepared from the corresponding iodide salt by anion-exchange with [NH4][PFg] in aqueous solution, as shown in Scheme 5.2-15. The iodide can be prepared as previously described by Stelzer et al. [73]. 

The Ir(III)-amido-hydrido complex 43 was isolated by reacting the electron-rich neutral phosphine-cyclooctene complex 42 according to Equation 6.13 [7] (note the cis arrangement of the hydride and amide function). Likewise, the cationic complex 44 reacted in neat aniline to afford a 50/50 mixture of the N—H (45) and C—H (46) activation products that was isolated as a light orange powder (Equation 6.14). Compound 45 was separated from 46 and purified in 49% overall yield. 

With the knowledge that 14 can activate aldehydes in 1, the role of 1 in the reaction was explored further. Specifically, the relative rates of C—H bond activation and guest ejection, and the possibility of ion association with 1, were investigated. The hydrophobic nature of 14 could allow for ion association on the exterior of 1, which would be both cn t h al pi cal I y favorable due to the cation-it interaction, and entropically favorable due to the partial desolvation of 14. To explore these questions, 14 was irreversibly trapped in solution by a large phosphine, which coordinates to the iridium complex and thereby inhibits encapsulation. Two different trapping phosphines were used. The first, triphenylphosphine tris-sulfonate sodium salt (TPPTS), is a trianionic water-soluble phosphine and should not be able to approach the highly anionic 1, thereby only trapping the iridium complex that has diffused away from 1. The second phosphine, l,3,5-triaza-7-phosphaadamantane (PTA), is a water-soluble neutral phosphine that should be able to intercept an ion-associated iridium complex. 

RhCl(PPh3) 3 The chlorine radical (Cl ) accepts an electron from rhodium metal (electronic configuration Ad1,5s2) to give Cl and Rh+. The chloride ion then donates two electrons to the rhodium ion to form a dative or a coordinate bond. Each PPh3 donates a lone pair of electrons on the phosphorus atom to the rhodium ion. The total number of electrons around rhodium is therefore 8 + 2 + 3X2=16, and the oxidation state of rhodium is obviously 1 +. The other way of counting is to take the nine electrons of rhodium and add one electron for the chlorine radical and six for the three neutral phosphine ligands. This also gives the same electron count of 16. 

The interaction of 5-block metals and phosphorus-based ligands takes many forms, from neutral phosphines and anionic diphosphides [PR] , to mixed (P,N) and (P,S) donors. The area has been one of intensive investigation, and there is praetieal interest in the use of sueh eompounds in organophosphorus synthesis. The area has witnessed eonsiderable growth prior to 1985, fewer than five eompounds containing an 5-block element bonded to phosphorus had been strueturally authentieated by the end of 2000, the total was over 200. Extensive reviews of the area have... 

The phosphine is a good soft nucleophile with a high-energy lone pair, well able to add in conjugate fashion without help. In particular, the neutral phosphine is a good nucleophile and . 

Note that in contrast to the complexes of SiCU with neutral phosphines, as shown above, the complexes with the carbanionic ligands C have at least one silicon-carbon bond. Apparently, this is enough to effectively make an additional P->Si donor-acceptor bond impossible. It is somewhat surprising that this is the case also in solution where an intramolecular P-Si bond should be particularly favored by the chelate effect. 

The neutral phosphonate esters, D(EB)[(EB)P], D(4-MPe-2)[BP], D(4-MPe-2)[(iB)P] and D(4-MPe-2)[PP] were prepared by the Michaelis-Arbuzov Reaction in which alkyl halides were reacted with previously prepared trialkyl phosphites. The neutral phosphate, T(4-MPe-2)P, was prepared by a conventional esterification method in which 4-methyl-2-pentanol was reacted with POCI3 in the presence of pyridine. The temperature during the reaction was kept below 15°C to prevent disproportionation of the alkyl group. The neutral phosphinate ester, B[DBP], was prepared by esterification of dibutyl phosphorus oxychloride, (C Hg)2P0C1, in the presence of pyridine. 

---