452. π-Complexes of biphenylene

Abstract

Biphenylene readily forms co-ordination compounds using one or both of its six-membered rings, but not its four-membered ring.BIPHENYLENE can be written with five Kekulb structures of which one represents it as a cyclobutane derivative (I), two as a cyclobutadiene derivative, and the remaining two as a cyclobutene derivative. In might therefore be expected to form co-ordination compounds by using either of its six-, or its four-membered ring. We have attempted to obtain both types of complex but succeeded in getting only the benzene type.When biphenylene is heated at 130" for 4 hr. with tricarbonyldiglymemolybdenum (4 mols.) [diglyme = 0 (CH,*CH,*OMe) , ] it readily forms scarlet p-biphenylenebis(tricarbonylmolybdenum) (11). The trans-arrangement is implied from the molecular centre of symmetry shown by the X-ray crystal data. This substance is stable in air and only sparingly soluble in hot organic solvents, giving solutions which rapidly decompose. Equimolecular proportions of the above reactants, heated at 100" for 64 hr., form orange tricarbonylbiphenylenemolybdenum , [C,,H,Mo (CO),] , soluble in organic solvents. [196l]n-Complexes of Biphenylene.

Stereochemical Control of Transition Metal Complexes by Polyphosphine Ligands

“…331 There have been numerous examples of reactions involving tdpme as tripodal ligand which can only be explained on the basis of an "arm-off" process during the course of the reaction which demonstrates the kinetic lability in contrast to the thermodynamic stability of the M-P bond in chelating polyphosphine It is still of some controversy, whether the aldehyde is formed by reaction of H2 with the acyl complex or if a hydrido complex transfers the hydride to the acyl moiety.12vM7 In the case of Rh(tdpme)(CO)H (209) evidence has been given for the reaction pathway with hydrogen, while the use of a binucleating tetraphosphine ligand system (E@C2WPh)&H2 (eLTTP) favors the hydride transfer from one metal to another. Catalysis, reactions of coordinated ligands, organometallic transformations, and structure and bonding can be represented with new perspectives because of polyphosphine ligands.…”

Electron-density studies of molecular magnetic materials

“…Remarkable insights into the metal±ligand coordination interactions have been earned from ED studies, more particularly in terms of L to M ' donation and M to L % back bonding according to the Dewar±Chatt±Duncanson model (Dewar, 1951;Chatt & Duncanson, 1953). This explanation of coordination bonds has been widely applied to metal porphyrins for example (Lecomte et al, 1986(Lecomte et al, , 1999.…”

Theoretical studies on structural and spectroscopic properties of photoelectrochemical cell ruthenium sensitizers, derivatives of AR20

“…In a simple Dewar, Chatt, and Duncanson model, [41] the bond interaction can be described as a donation from a r MO of the ligand (i.e., CN À or NCS À ) toward an empty d orbital of metal and a concurrent back-donation from a filled (or partially filled) d orbital to a p* antibonding orbital of the ligand. The two processes can promote and strengthen each other.…”