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Ligand Control of Agostic M...H...C Three-centre, Two-electron Bonding in Bicyclohept-2-yl Complexes of Platinum and Palladium. X-Ray Crystal Structures of 2-C7H10)(But2P(CH2(2PBut2)> and t2P(CH2)2PBut2)>

DOI: 10.1039/DT9910000863

Source and publish data:

Journal of the Chemical Society, Dalton Transactions p. 863 - 871 (1991)

Update date:2022-08-11

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Authors:

Carr, NicholasCarr, Nicholas

Dunne, Barry J.Dunne, Barry J.

Mole, LauraMole, Laura

Orpen, A. GuyOrpen, A. Guy

Spencer, John L.Spencer, John L.

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Article abstract of DOI:10.1039/DT9910000863

The reaction of non-co-ordinating acids with the Pt0 and Pd0 alkene complexes 2-C7H10)(L-L)> t2P(CH2)2PBut2, 1b or 1g; and o-C6H4(CH2PBut2)2, 11e or 1h; M = Pt, L-L = (C6H11)2P(CH2)2P(C6H11)2 1c or But2P(CH2)2PBut2 1d> affords a series of cationic bicyclo<2.2.1>hept-2-yl complexes 2a-2h in which the otherwise electron-deficient metal centre is stabilized by a three-centre two-electron (agostic) interaction with the exo-3-CH bond.The complexes were characterized by 1H, 13C and 31P NMR spectroscopy and for 1b and 2b by single-crystal x-ray crystallography.In complex 1b the norborn-2-ene is bound to the platinum in a normal in-plane η2-mode with equal Pt-C distances <2.110(7), 2.108(8) Angstroem> and Pt-P distances y2.273(2), 2.274(2) Angstroem>.For 2b the crystallographic results reveal a long Pt-Cβ contact of 2.309(5) Angstroem which is bridged by a hydrogen atom forming the agostic bond, whereas the Pt-Cα bond is shortened to 2.096(4) Angstroem.The Pt-P bond trans to the weak agostic bond is significantly shorter than the cis Pt-P bond <2.256(1) and 2.311(1) Angstroem, respectively>, and this asymmetry in the co-ordination of the diphosphine is reflected in the 31P NMR spectrum of 2b for which 1J(PtPtrans) >>> 1J(ptPcis).The extent of agostic interaction, as indicated by NMR parameters <1J(ptH), 1J(PtPtrans), etc.>, depends on the bite angle of the diphosphine and the bulk of the substituents on phosphorus such that the smallest diphosphines induce the strongest M...H...C interaction.All the agostic complexes undergo a rapid intramolecular rearrangement on the NMR time-scale at room temperature involving β-elimination and alkene rotation.However, the 31P nuclei remain non-equivalent up to 300 K.

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