A Bidentate Bisphosphine Functioning in Intramolecular Aliphatic Metalation and as an NMR Spectroscopic Probe for the...

The multistep synthesis of the novel diphosphine reference ligand L(2), 6, Ph(2)P(o-C(6)H(4)CH(2)C(6)H(4)-o)PPh(2), has been streamlined and can be prepared on a ca. 20 g scale. It forms metallacycles with a variety of metal fragments. The resulting, and very rigid, boat-boat conformation forces a proton (H(endo)()) of the bridging methylene in close proximity to the metal, which in turn renders these protons (H(endo)(), H(exo)()) diastereotopic. The NMR spectra of [L(2)MCl(2)] [M = Pd, 9; M = Pt, 10] and of the organometallic derived compounds [L(2)Pd(PPh(3))], 11, and [L(2)Pd(Cl)(eta(2)-CH(2)Ph)], 12, consist of a pair of doublets, with the H(endo)() coupled to the P of the metallacycle. The CH(2)-metal close proximity drives the electrophilic metalation of the bridging methylene by RhCl(3) to form [L(2)Rh(Cl)(2)(MeCN)], 13, [L(2) = Ph(2)P(o-C(6)H(4)CHC(6)H(4)-o)PPh(2)]. A significant example, which shows how the coordination number of the metal can affect the H(exo)()-H(endo)() resonance separation, is provided by the couple [L(2)Ni(C(2)H(4))], 14, and [L(2)Ni(CO)(2)], 15. In order to show that the metallacycle size is crucial for the bridging methylene to function as a spectroscopic probe, we complexed the same [Fe(CO)(3)] fragment to L(2), 6, and L'(2), 17, [L'(2) = Ph(2)PO(o-C(6)H(2)(4,6Bu(t)(2))CH(2)(4,6Bu(t)(2))C(6)H(2)-o)OPPh(2)], to give [L(2)Fe(CO)(3)], 19, and [L'(2)Fe(CO)(3)], 18, respectively. In complex 17 the diastereotopic nature of these protons and hence the spectroscopic information was lost because of the presence of a 10-membered metallacycle. Crystal data: 9 is triclinic, space group P&onemacr;, a = 11.987(1) Å, b = 15.990(2) Å, c = 10.872(1) Å, alpha = 91.42(1) degrees, beta = 111.01(2) degrees, gamma = 99.86(2) degrees, V = 1908.2(5) Å(3), Z = 2, and R = 0.053; 11 is monoclinic, space group C2/c, a = 39.071(5) Å, b = 13.657(4) Å, c = 19.848(5) Å, beta = 92.45(2) degrees, V = 10581(5) Å(3), Z = 8, and R = 0.047; 12 is triclinic, space group P&onemacr;, a = 11.289(1) Å, b = 18.769(2) Å, c = 11.077(1) Å, alpha = 91.20(1) degrees, beta = 111.27(1) degrees, gamma = 105.26(1) degrees, V = 2107.7(4) Å(3), Z = 2, and R = 0.039; 13 is orthorhombic, space group P2(1)2(1)2(1), a = 15.346(2) Å, b = 18.188(3) Å, c = 12.072(2) Å, V = 3369.5(9) Å(3), Z = 4, and R = 0.042.