Acetylenic Carbon-13 Chemical Shift Tensors for Diphenylacetylene and (η2-Diphenylacetylene)Pt(PPh3)2: A Solid-State NMR and Theoretical Study

QUANTUM CHEMISTRY STUDIES ON THE Fe-Hg INTERACTIONS AND 31P NMR IN [Fe(CO)3(RPhPpy)2 (HgCl2)] (R = Me, Et, Ph)

In order to study the effects of R group on Fe-Hg interactions and 31P NMR, the structures of mononuclear complexes [Fe(CO)3(RPhPpy)2] (1: R = Me; 2: R = Et; 3: R = Ph) and binuclear complexes [Fe(CO)3(RPhPpy)2(HgCl2)] (4: R = Me; 6: R = Et; 6: R = Ph) were calculated by density functional theory (DFT) PBE0 method. Moreover, the 31P NMR chemical shifts were calculated by PBE0-GIAO method. The replacement of Ph group in Ph2Ppy ligands with Me or Et group results in higher stabilities and stronger Fe-Hg interactions. The stabilities of binuclear complexes follow the order of 5 > 4 >6. Although the electrostatic interactions in 5 are weaker, the weaker repulsion interactions and stronger orbital interactions lead to the highest stability. The strength of Fe → Hg interactions, which mainly attribute to σFe-P → nHg and σFe-C → nHg charge-transfer interactions, follows the order of 5 > 4 > 6. The 31P NMR chemical shifts in mononuclear complexes 1 ~ 3 or binuclear complexes 4 ~ 6 increase with the increase of electron-withdrawing effect of R group following the order of Me < Et < Ph. Due to Fe → Hg interactions, the charge-transfer from R groups towards the P , Fe and Hg atoms increases the electron density on P nucleus in binuclear complexes. Besides, the stronger σFe-C → nP charge-transfer in binuclear complexes can also increase the electron density of P nucleus. As a result, compared with corresponding mononuclear complexes, the 31P chemical shifts in binuclear complexes show some reduction.

Activation of Acetylene by Coordination to Bis-Triphenylphosphine Complex of Pt(0): DFT Study

The present work is devoted to the theoretical study of the activation of the acetylene molecule coordinated in the [Pt(PPh3)2C2H2] complex. By means of DFT calculations it is shown that the geometrical and electronic characteristics of the C2H2 are essentially changed due to its coordination. The subsequent detailed analysis of the molecular orbitals (MO) of the active valence zone of this complex allows one to make important conclusion that this activation is being realized mainly due to the orbital back donation of 5d-electronic density from one of the occupied MOs of the complex [Pt(PPh3)2] to the unoccupied antibonding π*-MO of C2H2.

Probing lead(II) bonding environments in 4-substituted pyridine adducts of (2,6-Me2C6H3S)2Pb: an X-ray structural and solid-state 207Pb NMR study

The effect of subtle changes in the sigma-electron donor ability of 4-substituted pyridine ligands on the lead(II) coordination environment of (2,6-Me(2)C(6)H(3)S)(2)Pb (1) adducts has been examined. The reaction of 1 with a series of 4-substituted pyridines in toluene or dichloromethane results in the formation of 1:1 complexes [(2,6-Me(2)C(6)H(3)S)(2)Pb(pyCOH)](2) (3), [(2,6-Me(2)C(6)H(3)S)(2)Pb(pyOMe)](2) (4), and (2,6-Me(2)C(6)H(3)S)(2)Pb(pyNMe(2)) (5) (pyCOH = 4-pyridinecarboxaldehyde; pyOMe = 4-methoxypyridine; pyNMe2 = 4-dimethylaminopyridine), all of which have been structurally characterized by X-ray crystallography. The structures of 3 and 4 are dimeric and have psi-trigonal bipyramidal S(3)N bonding environments, with the 4-substituted pyridine nitrogen and bridging sulfur atoms in axial positions and two thiolate sulfur atoms in equatorial sites. Conversely, compound 5 is monomeric and exhibits a psi-trigonal pyramidal S(2)N bonding environment at lead(II). The observed structures may be rationalized in terms of a simple valence bond model and the sigma-electron donor ability of the 4-pyridine ligands as derived from the analysis of proton affinity values. Solid-state (207)Pb NMR experiments are applied in combination with density functional theory (DFT) calculations to provide further insight into the nature of bonding in 4, 5, and (2,6-Me(2)C(6)H(3)S)(2)Pb(py)(2) (2). The lead chemical shielding (CS) tensor parameters of 2, 4, and 5 reveal some of the largest chemical shielding anisotropies (CSA) observed in lead coordination complexes to date. DFT calculations using the Amsterdam Density Functional (ADF) program, which take into account relativistic effects using the zeroth-order regular approximation (ZORA), yield lead CS tensor components and orientations. Paramagnetic contributions to the lead CS tensor from individual pairs of occupied and virtual molecular orbitals (MOs) are examined to gain insight into the origin of the large CSA. The CS tensor is primarily influenced by mixing of the occupied MOs localized on the sulfur and lead atoms with virtual MOs largely comprised of lead 6p orbitals.

Solid-State 139La and 15N NMR Spectroscopy of Lanthanum-Containing Metallocenes

A preliminary set of solid-state 139La and 15N NMR data for lanthanum-containing metallocenes is presented, including (C5H5)3La, (C5Me4H)3La, [(C5Me5)2La]+[BPh4]-, and 15N-enriched [(C5Me4H)2La(THF)]215N2. Broad 139La NMR spectra, with breadths ranging from 600 kHz to 2.5 MHz, were acquired with piecewise QCPMG techniques at 9.4 T. Simulations of the spectra reveal 139La quadrupolar coupling constants (CQ) between 44 and 105 MHz. In addition, the first NMR measurement of a nitrogen chemical shift (CS) tensor for dinitrogen bound side-on to a metal atom is reported for [(C5Me4H)2La(THF)]215N2. The 139La NMR parameters show remarkable sensitivity to changes in metallocene structure and can be interpreted in an intuitive manner. Preliminary RHF and DFT calculations of 139La electric field gradient (EFG) and nitrogen CS tensors are used to provide tensor orientations and to rationalize the origin of the NMR parameters in terms of molecular structure and symmetry. The sensitivity of 139La and 15N NMR tensor parameters to changes in structure and bonding should prove invaluable in future studies of noncrystalline and disordered systems.