Mechanisms and kinetics of the elementotropic rearrangements of tetrahydro-4,4,8,8-tetramethyl-4,8-disila-sym-indacene

Abstract

The dynamic stereochemistry of silatropic rearrangements of tetrahydro-4,4,8,8-tetramethyl-4,8-disi[a-sym-indacene (dimer of 6,6-dimethyl-6-silafulvene), which exists in solution a.s an equilibrium rnixmre of two interconverting isomers, was studied. The mechanisms and complete kinetic scheme of rearrangements were established using IH, taC, and 29Si 2D quantitative EXSY NMR spectroscopy. It was tbund that the interconversion and degenerate rearrangements of the observed isomers proceed via two concurrent pathways due to the formation of different intermediates. The activation parameters of the rearrangements were determined by means of total lineshape analysis of dynamic NMR (DNMR) spectra.

Synthesis and reactions of organometallic complexes featuring a doubly-linked dicyclopentadienyl ligand

“…The doubly-linked dicyclopentadienyl {(^-CgHs^SiMezb} (3) dianion is a rigid system that allows the coordination of two metal fragments that occupy cis or trans positions with respect to the faces of the rings, a quality that gives rise to the structural motifs A and B.…”

“…After vacuum removal of the solvents from the above three eluates, the residues were recrystallized from hexanes (eluates 1 and 3) or hexanes/CH2Cl2 1:1 13 C NMR (100 MHz,6.76,8.27 (CH 3 ), 63. 21,81.53,86.78,89.02,89.06,93.87,96.93,98.71,98.78,104.99 (Cp;10 peaks),110.19,116.27,117.20,126.84,125.90,125.95,126.00,126.08,126.49,126.70,127.36,127.72,131.33,131.54,132.47,134.25,134.99,135.20,139.88,140.74,141.95,155.11,175.58 21,94.71,95.50,107.98,108.03,109.48,110.125 (Cp),125.44,128.47,138.68,141.00 (Ph),201.02,202.11,241.36 (CO) 2787.6(3) z 4 crystal color, habit orange plate crystal size, mm 0.43 x 0.35 x 0.03 Z) (calcd), g cm" 3 1.705 wavelength, Â 0.7...…”

“…and some reactions give formamides and ureas catalytically. 3 One approach to making a complex more positive is to add a proton (KT) to the metal (eq 2). While numerous metal carbonyl complexes have been protonated, 4 the CO ligands in these complexes either do not react with amines because their kco and v(CO) values are insufficiently high or the amine…”

“…NHR with amines are also known to give formamides, 3 carbamates, 4 and ureas, 5 either stoichiometrically or catalytically.…”

“…Complex Iff 1 ', [ {(7 5 -CsH3)2(SiMe2)2}Ru2(CO)4(t/-H)] + , with a protonated Ru-Ru bond, is deprotonated only very slowly (hours or days) by basic amines and phosphines although the proton in Iff 1 " is acidic thermodynamically. This remarkable kinetic inertness of the bridging proton allows primary and secondary amines to react with 1H* by attacking the CO ligand to give a formamide and the CO-substituted ruthenium complex ({^-CgHsMSiMeih}-Ru 2 (NHR l R 2 )(CO) 3 . We have demonstrated that a CO ligand in the protonated complex {(^5-CsH3)2(SiMe2) 2 } Ru 2 (CO)4(//-H)] + (lHT ") is the site of reaction with amines because of the high electrophilicity of the CO ligands and the low kinetic acidity of the bridging hydride -a unique combination of kinetic properties that are not found in the Fe and Os analogs.…”