Deprotonation of η²(4e)-bonded alkynes as a pathway to σ,η²(3e)-prop-2-ynyl, η⁵-pentadienyl and η⁴-trans-1,3-diene substituted molybdenum complexes

Ruthenium Tripyrazolylborate Complexes. 8. trans-Diene Coordination in Ruthenium Tripyrazolylborate Complexes

“…Furthermore, the diene ligand exhibits a short−long−short pattern of C−C distances (1.297(5) vs 1.450(8) Å). A similar pattern is found in other examples of s-trans -diene coordination. − There are, however, also trans -1,3-diene complexes which show almost equal C−C bond lengths . The structure of 4 , depicted in Figure , is very similar to that of 2 .…”

Quantitative Determination of the Regioselectivity of Nucleophilic Addition to η3-Propargyl Rhenium Complexes and Direct Observation of an Equilibrium between η3-Propargyl Rhenium Complexes and Rhenacyclobutenes

“…Green has reported Extended Hückel Molecular Orbital calculations (EHMO) on the neutral η 3 -propargyl molybdenum complex C 5 H 5 ( η 2 -HC≡CH)Mo( η 3 -CH 2 C≡CH) 29. Although the regiochemistry of nucleophilic addition was not commented upon, the EHMO results indicated a significant difference in calculated atomic charges between the center (positive) and terminal (negative) carbons, which might form the basis of a charge-controlled explanation of addition of nucleophiles to the center carbon.…”

Synthesis and reactivity of η2(4e)-alkyne and η2(3e)-vinyl complexes of rhenium

“…The rheniumcentred cation carries q5-C5H,, PMePh,, bromo and q2-PhC,Ph ligands, the alkyne C-C vector lying parallel to the rhenium-bromide bond, thus maximising back bonding from the metal fragment HOMO (highest occupied molecular orbital) to the alkyne antibonding orbitals. It is interesting that the alkyne C-C bond length [C( 1)-C(2) 1.26(4) A] is short, being similar to that reported * for the oxorhenium complexes [Re(0)I(q2-MeC,Me),] [average 1.283(7) A], [Re0(q2-Me-C,Me),(py)J[SbF,] (py = pyridine) [average 1.285(6) A], and the cationic nitrosyl complex [Re(NO)(q2-EtC,Et)(PPh,)(q-C,H,)][BF,] [1.24 (1) but significantly (0.07 A) shorter than that found in the q2(4e)-bonded hex-3-yne complex [ReCl,jq2-EtC,Et)(q-C5Me5)] [1.326(4) A]. Examination of the bond-length data shows that the q-C,H, ligand is tilted relative to the rhenium atom as is reflected in the atom separations Re-C(28) 2.21(3), Re-C(29) 2.14(3), Re-C(30) 2.33(3), Re-C(31) 2.37(3), and Re-C(32) 2.34(3) A.…”