Rhenium Oxo Complexes of a Chelating Diyne Ligand. Synthesis and Study of the Kinetics of Protonation

Abstract

A series of oxo complexes, Re(O)X(diyne) (X = I, Me, Et), have been prepared from 2,7-nonadiyne and Re(O)I(3)(PPh(3))(2). Addition of B(C(6)F(5))(3) to Re(O)I(2,7-nonadiyne) (5) results in coordination of the oxo ligand to the boron. The protonation of Re(O)(X)(2-butyne)(2) and Re(O)(X)(2,7-nonadiyne)(2) with a variety of acids has been examined. With 5 and HBF(4)/Et(2)O, the ultimate product was [Re(CH(3)CN)(3)(I)(2,7-nonadiyne)](2+) (7). The conversion of 5 to 7 changes the conformation of the diyne ligand from a "chair" to a "boat" and shifts its propargylic protons considerably downfield in the (1)H NMR. The kinetics of the protonation of Re(O)I(2,7-nonadiyne) (5) by CF(3)SO(3)H in CH(3)CN have been monitored by visible spectroscopy, in a stopped-flow apparatus, and by low temperature (1)H NMR. Two second-order rate constants, presumably successive protonations, were observed in the stopped-flow, k(1) = 11.9 M(-)(1) s(-)(1) and k(2) = 3.8 M(-)(1) s(-)(1). Low temperature (1)H NMR spectroscopy indicated that the resulting solution contained a mixture of two doubly protonated intermediates X and Y, each of which slowly formed the product 7 via an acid-independent process.

η2‐Iminoacyl and η2‐Acyl Monocyclopentadienyl Tantalum Complexes Bearing Oxo and Oxo‐Borane Ligands

“…All the values of the bond lengths and angles of compound 2d are very close to the corresponding bond lengths and angles found for the parent compound [TaCp*Cl{η 2 -C(Me)=NAr}(O)] [10] except for the Ta [ [21][22][23][24][25][26][27][28][29][30][31] The Ta-O bond in 2d is longer than that in the oxo-borane compound [TaCp*Cl 2 {O·B(C 6 F 5 ) 3 }] [21] [1.784(2) Å]. This bond length is similar to the lower end of the range of Ta-O bond lengths for compounds with Ta-O-Ta bridges (1.82-2.10 Å) [32][33][34][35] and with terminal Ta-OH bonds (1.85-1.97 Å).…”

“…[10,11] The versatility and potential applications of all these results determined by the R and X substituents of the imido complexes [TaCp*MeX(NR)] led us to extend our studies to similar insertion reactions of CNR and CO into the Taalkyl bonds of the related oxo-borane compounds [TaCp*X 2 {O·B(C 6 F 5 ) 3 }] that have recently been isolated. [21] Results and Discussion [21][22][23][24][25][26][27][28][29][30][31] and the 1 H NMR spectra with the monosubstitution of only one of the alkyl ligands. These pale yellow complexes are air and thermally stable in solution.…”

“…The Ta have values that are normally seen for these types of compounds. [21][22][23][24][25][26][27][28][29][30][31] The whole set of angles and bond lengths of the [Ta-(η 2 -acyl)] group is in line with compounds of this type [1] and is similar to those found in the other two tantalum-acyl complexes for which X-ray structures are known, [TaCp*Me{η 2 -C(CH 2 CMe 2 Ph)=O}{N(2,6-Me 2 C 6 H 3 )}] [39] and [TaCp*Cl 3 {η 2 -C(CH 2 CMe 3 )=O}]. [40] However, in the particular case of the isostructural imido derivative [TaCp*Me{η The insertion of a second CNAr or CO molecule into these new acyl and iminoacyl oxo-borane complexes was not observed, in contrast with the behaviour observed for the analogous tert-butyl imido complexes.…”

Interaction of Metal Oxido Compounds with B(C6F5)3

“…[33][34][35][36][37] However,i ts eems that in lower valent complexes, the influence is smaller as in the rhenium(III) compound [Re III {OB(C 6 F 5 ) 3 }(2,7-nonadiyne)] (15)o nly aR e =Oe longation from 1.692(4) to 1.724(3) occursu pon borane coordination. [41]…”

Iron-Catalyzed Formation of 2-Aminopyridines from Diynes and Cyanamides

“…Iron Chloride (99.95% purity) was purchased from Alfa Aesar. Diynes 1a , 27 1b-c , 28 1d , 29 1e , 30 1f , 31 1g , 32 1h , 33 1i , 34 and 1j-k 35 were prepared from known literature procedures. Liquid cyanamides were degassed using three sequential freeze-pump-thaw cycles.…”