Brian Weeks

Transition metal–carbon bonds. Part 52. Large ring and cyclometallated complexes formed from But2PCH2CH2CHRCH2CH2PBut2(R H or Me) and IrCl3, or [Ir2Cl4(cyclo-octene)4] : crystal structures of the cyclometallated hydride, [IrHCl(But2PCH2CH2CHCH2CH2PBut2)], and the carbene complex [IrCl(But2PCH2CH2CCH2CH2PBut2)]

Treatment of But2P(CH2)5PBut2, with iridium trichloride gives a mixture of the 16-atom ring dihydride [lr2H2Cl4{But2P(CH2)5PBut2}2], a co-ordinatively saturated cyclometallated hydride, [[graphic omitted]But2)])(1b), which is non-fluxional, and an unidentified complex. A better route to the cyclometallated hydride (1b) is to treat [Ir2Cl2(C8H14)4](C8H14= cyclo-octene) with the diphosphine. Complex (1b) takes up carbon monoxide to give the six-co-ordinate [[graphic omitted]But2)] and loses dihydrogen on heating [ca. 200 °C (15 mmHg)] to give the very dark carbene/ylide complex [[graphic omitted]But2)](3)/(4). This carbene/ylide complex takes up dihydrogen at 20 °C (1 atm) to give back (1b). The diphosphine But2PCH2CH2CHMeCH2CH2PBut2 reacts with IrCl3 to give the 16-atom ring chelate [Ir2H2Cl4(But2PCH2CH2CHMeCH2CH2 PBut2)2], no cyclometallated product being detected. However, the complex [[graphic omitted]But2)], can be prepared from [Ir2Cl2(C8H14)4] and the diphosphine. Hydrogen-1, 13C, and 31P n.m.r. and i.r. data are reported. The crystal structures of (1b) and of the carbene/ylide (3)/(4) have been determined. Cell dimensions are, for (1b), a= 1 231.8(3), b= 1 435.9(3), c= 1 485.4(3) pm, and β= 104.82(2)° and for (3)/(4), a= 1 232.6(3), b= 1 436.2(3), c= 1 480.7(3) pm, and β= 104.87(2)°. The structures are isomorphous, with space group P21/c and Z= 4.

Formation of large chelate rings and cyclometallated products from diphosphines of type But2P(CH2)nPBut2(n= 5–8) and Ph2P(CH2)5PPh2 with palladium and platinum chlorides: factors affecting the stability and conformation of large chelate rings

The new diphosphines But2P(CH2)nPBut2(n= 5–7) are described and the previously known Ph2P(CH2)5PPh2 characterized more fully. The compounds, But2P(CH2)nPBut2(n= 5–8) react with [PdCl2(NCPh)2] to give crystalline complexes of the type [{PdCl2[But2P(CH2)nPBut2]}x], where x= 2 for n= 5, 7, or 8 but unknown for n= 6. Also for n= 5 a volatile cyclometallated complex [[graphic omitted]But2)] is formed. With [PtCl2(NCPh)2] or [PtCl2(NCBut)2], But2P(CH2)5Pbut2 gives trans-[{PtCl2[But2P(CH2)5PBut2]}x](x is unknown) and a cyclometallated product [[graphic omitted]But2)](X = Cl) contaminated by a very similar species, possibly [[graphic omitted]But2)] from which it could not be separated. The complex [{PtCl2[But2P(CH2)5PBut2]}x] with CF3CO2H, however, gives pure [[graphic omitted]But2)](X = O2CCF3) in almost quantitative yield and other pure complexes of this type with X = Cl, Br, I, or H are readily prepared by metathesis. The compound But2P(CH2)6PBut2 with [PtCl2(NCPh)2] gives trans-[{PtCl2[But2P(CH2)6PBut2]}x](x is unknown) and the cyclometallated [[graphic omitted]But2)]. A remarkable difference in extent of deuteriation is observed on treating [[graphic omitted]But2)](X = Cl or Br) with CF3CO2D. The chloro-complex is not deuteriated but the bromo-complex is deuteriated in both t-butyl and methylene groups. Using 31P n.m.r. spectroscopy the large-chelate mixed compounds described in this and previous papers, containing PBut2 groups in ‘corner’ positions, are shown to be stable in solution relative to open-chain structures. The complexes trans-[Pd2Cl4{Ph2P(CH2)5PPh2}2] and cis-[Pt2Cl4{Ph2P(CH2)5PPh2}2] are described. The literature on large-chelate-ring compounds is surveyed. Factors affecting the stability and conformational homogeneity of carbocyclic and hetero-substituted rings, cyclic peptides, and depsipeptides, and cyclic monomer–polymer equilibria are discussed. Since the effects of sterically demanding substituents on the stability of purely organic rings (large and otherwise) has been explained purely in terms of bond lengths, angles, torsion angles, etc., sterically demanding substituents must have similar effects on chelate rings. Enthalpy and entropy factors affecting the stability of large chelate rings and their conformational homogeneity in solution are discussed from this point of view. Infrared, 1H, 13C, and 31P n.m.r., and mass spectral data are given and discussed.

Synthesis and X-ray structure of an unusual iridium ylide or carbene complex

IrCl3 reacts with But2P[CH2]5PBut2 to give [[graphic omitted]] which loses dihydrogen reversibly to give [[graphic omitted]], the structure of which has been determined by X-ray diffraction.

Large ring compounds involving trans-bonding bidentate ligands

Large ring mononuclear compounds of platinum and iridium involving the trans-co-ordinating ligands But2P[CH2]xPBut2(x= 9 or 10), and large ring binuclear complexes are described; it is suggested that mononuclear bidentate complexes with a large ring might be more stable than those with an intermediate size ring.

Large-ring complexes of platinum and palladium of the type trans-[{MCl2[But2P(CH2)nPBut2]}x]

Large-ring (12- to 45-membered) complexes of the type trans-[{MCl2[But2P(CH2)nPBut2]x}](M = Pt or Pd; n= 8, 9, 10, or 12: x= 1–3) are formed by treating [MCl2(NCPh)2] with the flexible long-chain diphosphines. The mononuclear (x= 1) complexes of platinum are volatile and have also been studied by mass spectrometry. 1H and 31P N.m.r. data are given as are values of (M–Cl). Bond length and bond angle data for the binuclear complex [{PdCl2[But2P(CH2)10PBut2]}2], with a 26-membered ring, are also given.

Internal metallation of N- or P-donor bidentate ligands to give multidentate oraganometallic compounds

Bidentate di-N- or di-P-donors are internally metallaed by platinum or palladium very much less readily than analogous monodentate ligands but metallation can be promoted by increasing the chelate ring size from five to six and by using certain reagents.