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Activation and Functionalization of White Phosphorus at Rhodium: Experimental and Computational Analysis of the [(triphos)Rh (η 1 :η 2 ‐P 4 RR′)]Y Complexes (triphos=MeC(CH 2 PPh 2 ) 3 ; R=H, Alkyl, Aryl; R′=2 Electrons, H, Me)
Author(s) -
Barbaro Pierluigi,
Ienco Andrea,
Mealli Carlo,
Peruzzini Maurizio,
Scherer Otto J.,
Schmitt Guido,
Vizza Francesco,
Wolmershäuser Gotthelf
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200305091
Subject(s) - triphos , chemistry , regioselectivity , aryl , rhodium , medicinal chemistry , alkyl , stereochemistry , electrophile , ligand (biochemistry) , molecule , organic chemistry , catalysis , biochemistry , receptor
Thermal reaction of white phosphorus with [(triphos)RhH 3 ] ( 1 ) in THF affords [(triphos)Rh(η 1 :η 2 ‐P 4 H)] ( 2 ), triphos=MeC(CH 2 PPh 2 ) 3 . Similar complexes [(triphos)Rh(η 1 :η 2 ‐P 4 R)] (R=Me ( 7 ), Et ( 8 ), Ph ( 9 )) also form at lower temperature by the reaction of P 4 and [(triphos)Rh(R)(η 2 ‐C 2 H 4 )] with elimination of ethene. In contrast, a double‐insertion process follows the reaction of [(triphos)Rh(H)(η 2 ‐C 2 H 4 )] and P 4 to generate tetraphosphido ethyl complex 8 . Compounds 2, 7, 8 and 9 are thermally unstable and eventually decompose into the cyclotriphosphorus complex [(triphos)Rh(η 3 ‐P 3 )] ( 3 ) plus other unidentified phosphorus‐containing species. Otherwise, PH 3 or PH 2 R is generated in the presence of H 2 . The formation of PH 3 and 3 is quantitative starting from the precursor 2 . The electrophilic attack of MeOTf or HBF 4 on the P 4 R ligand in the complexes 2, 7 – 9 is regioselective, and yields a cationic product of formula [(triphos)Rh(η 1 :η 2 ‐P 4 RR′)] + . The direct attack on the substituted p ‐R phosphorus atom is demonstrated by crossing experiments. Complexes of the latter type have been isolated in the solid state for the combinations R=H and R′=Me ( 11 ) or R=Ph and R′=Me ( 12 ). The latter species, [(triphos)Rh(η 1 :η 2 ‐P 4 PhMe′)]OTf ⋅ 2 CH 2 Cl 2 (OTf=triflate), has been characterised by X‐ray methods. The geometry at the metal is better described as a trigonal bipyramidal than pseudo‐octahedral. In fact, the P 4 RR′ unit acts as a bidentate ligand with its exocyclic PR 2 donor group and the endocyclic, dihapto‐coordinated PP linkage. The latter group lies in the equatorial plane, in a similar way to a classic olefin ligand that is coordinated to a butterfly‐shaped L 4 M fragment (M=d 8 ). DFT calculations on a model of 2 and all possible protonated isomers confirm that double substitution at the exocyclic P‐donor positions of the open P 4 unit is energetically favoured. A multinuclear and multidimensional NMR analysis confirms that this structure is maintained in solution for both the parent and the protonated compounds.