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Ivan S Podkorytov

Publications and source records attributed to Ivan S Podkorytov.

3 recordsLinked to original sources
PubMed2004

Synthesis and structural characterization of two novel heterometallic clusters: [Rh4Pt2(CO)11(dppm)2] and [Ru2Rh2Pt2(CO)12(dppm)2].

Two novel heterometallic octahedral clusters [Rh(4)Pt(2)(CO)(11)(dppm)(2)](1) and [Ru(2)Rh(2)Pt(2)(CO)(12)(dppm)(2)](2) were synthesized by the reaction of [Rh(2)Pt(2)(CO)(6)(dppm)(2)] with [Rh(6)(CO)(14)(NCMe)(2)] and Ru(3)(CO)(12), respectively. Solid state structures of 1 and 2 have been established by a single crystal X-ray diffraction study. Two dppm ligands in 1 are bonded to one platinum and three rhodium atoms, which form an equatorial plane of the Rh(4)Pt(2) octahedron. Two rhodium and two platinum atoms bound to the diphosphine ligands in 2 are nonplanar to give an octahedral C2 symmetric Ru(2)Rh(2)Pt(2)(dppm)2 framework. The (31)P NMR investigation of and (1D, (31)P COSY, (31)P-[(103)Rh] HMQC) and simulation of 1D spectral patterns showed that in both clusters the structures of the M(6)(PP)(2) fragments found in the solid state are maintained in solution.

Journal Article↗
PubMed2004

Microsecond time-scale dynamics from relaxation in the rotating frame: experiments using spin lock with alternating phase.

A spin lock comprised of radiofrequency pulses with alternating phase, (x) (-x)(x) (-x) , is proposed as a new technique to probe microsecond time-scale dynamics. A series of R1rho measurements using different pulse duration tp allows one to determine exchange rate, kex, the product p(a)p(b)(Delta omega(ab))2 involving populations of the exchanging species, p(a) and p(b), together with chemical shift difference, (Delta omega(ab)), and the strength of the spin-lock field, B1. The interpretation is based on simple analytical expression for R1rho derived on the basis of Redfield theory. The application of the method is demonstrated for partially deuterated molecule of cyclohexane undergoing chair-to-chair interconversion at -9 degrees C.

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PubMed2002

Tripyrrolylphosphine as a unique bridging ligand in the Rh6CO14(mu2-P(NC4H4)3) cluster: structure, bonding, fluxionality, thermodynamics, and kinetics studies.

Tripyrrolylphosphine reacts with the cluster Rh6CO15(NCMe) to afford the disubstituted Rh6CO14(mu2)-P(NC4H4)3) derivative (2) via the Rh6CO15P(NC4H4)3 intermediate (1) with eta(1)-P coordination. In the solid state, 2 has the phosphine occupying a bridging position where it is bonded to two neighboring Rh atoms in the Rh(6) octahedron through the P-atom and an approximately tetrahedral alpha-carbon atom of one of the pyrrolyl rings. This can be described by the interaction of an electron pair, associated with a negative charge on one of the canonical forms of the NC(4)H(4) ring, with the adjacent Rh center. (1)H NMR spectra show that the solid-state structure is retained in solution, but the phosphine is not rigid, and three distinctive dynamic processes are observed. Each of these represents independent hindered rotation of inequivalent pyrrolyl rings about P-N bonds, the ring involved in the interaction with the Rh(6) skeleton displaying the highest activation barrier with deltaH = 15.8 +/- 0.1 kcal mol(-1) and deltaS = 1.4 +/- 0.3 cal K(-1) mol(-1). The assignment has been confirmed by 1H TOCSY and EXSY experiments, and a mechanism is proposed. The formation of 2 from 1 is reversible in the presence of CO, which is highly unusual for bridged clusters. The kinetics of the forward and reverse reactions have been studied, and the values of DeltaH degrees and DeltaS degrees for formation of 2 (+1.3 +/- 0.5 kcal mol(-1) and -9 +/- 2 cal K(-1) mol (-1), respectively) show that the Rh-C bond in the bridge is comparable in strength with the Rh-CO bond it replaces. The intrinsic entropy of 2 is exceptionally unfavorable, overcoming the favorable entropy caused by CO release, and this allows the reversibility of bridge formation. The reactions proceed via a reactive intermediate that may involve agostic bonding of the ring. The reverse reaction has an exceedingly unfavorable activation entropy that emphasizes the unique nature of 2.

Journal Article↗