Synthesis, spectroscopic characterization, X-ray structure and DFT calculations of p-tolylimido rhenium(V) complexes of 2,2′-dipyridylamine

p-Tolylimido rhenium(v) complexes with phenolate-based ligands: synthesis, X-ray studies and catalytic activity in oxidation with tert-butylhydroperoxide

“…For all compounds 1-16, the ν(Re-NTol) stretches are extremely difficult to identify as these vibrations are mixed with ν CvN and ν P-C modes of PPh 3 and N-O ligands. 18,19,22,23 The 1 H NMR spectra of 1-6 confirmed the occurrence of only one isomer in solution. Distinctive signals attributed to the alkyl protons of the p-tolylimido group of 2-16 and methyl groups attached to the phenolate ring of the hmpbta ligand in 2, 7, 8, 11 and 12 occur in the ranges 2.37-2.…”

“…Compared with the rhenium(V) imido complexes of carboxylate-based ligands, 18a-c 20 [ReO(hmbzim) 2 (PPh 3 )](ReO 4 ) 21 and [Re( p-NTol)X(OMe)(Hdpa)(PPh 3 )]ReO 4 . 22 In both acetonitrile and methanol, the initial step of the complex formation seems to involve the substitution of the oxygen atom of the N,O-donor ligand (HL 1 , HL 2 and HL 3 ) for the labile X ligand trans to the imido group in [Re( p-NTol)-X 3 (PPh 3 ) 2 ], possibly with the proton transfer to give the monodentate intermediate A (Scheme 3). In the next step, the unco- ordinated N-donor atom of the N,O-donor ligand would either substitute the equatorial halide to form monocationic complexes [Re( p-NTol)X(L)(PPh 3 ) 2 ]X or substitute one of the equatorial phosphine ligands to form neutral imido complexes trans…”

“…For both cis-(X,X) and trans-(X,X) isomers of [Re( p-NTol)X 2 (L)(PPh 3 )], the Re-N imido -C imido bond angle of 175.99(18)°in 1, 18d 174.3(3)°in 2, 170.5(4)°in 3, 174.8(3)°in 4, 3)°in 6 agrees with a linear coordination mode of the arylimido ligands (167-176°), and it is typical of phenyl imido ligands in high oxidation state complexes, in which the metal is relatively electron-deficient and some π-bonding between the imido nitrogen atom and the metal exists. 18,19,22,23 The Re-N imido bond lengths of 1.7195(20) Å in 1, 18d 1.723(4) Å in 2, 1.704(5) Å in 3, 1.725(3) Å in 4, 1.721(2) Å in 5 and 1.722(4) Å in 6 fall in the range typical of mononuclear complexes of rhenium(V) having a [RevNR] 3+ core. 18,19,22,23 The interatomic distances between the rhenium atom and phenolate oxygen atom of 1.9881(17) Å in 1, 18d 1.997(3) Å in 2, 2.008(4) Å in 3, 2.016(3)Å in 4, 2.0113(18) Å in 5 and 2.004(3) Å in 6 reflect the single bond character, 24 indicating only slight electron delocalization in the RNvRe-O unit.…”

“…18,19,22,23 The Re-N imido bond lengths of 1.7195(20) Å in 1, 18d 1.723(4) Å in 2, 1.704(5) Å in 3, 1.725(3) Å in 4, 1.721(2) Å in 5 and 1.722(4) Å in 6 fall in the range typical of mononuclear complexes of rhenium(V) having a [RevNR] 3+ core. 18,19,22,23 The interatomic distances between the rhenium atom and phenolate oxygen atom of 1.9881(17) Å in 1, 18d 1.997(3) Å in 2, 2.008(4) Å in 3, 2.016(3)Å in 4, 2.0113(18) Å in 5 and 2.004(3) Å in 6 reflect the single bond character, 24 indicating only slight electron delocalization in the RNvRe-O unit. A noticeable difference in Re-O(1) and Re-N( 1) of 1-6 can be understood in terms of Pearson's hard-soft acid-base theory.…”

“…19,20,23,24 The Re-N imido bond lengths of 7-10 and 13-16 [1.731(4) Å in 7, 1.741(5) Å in 8, 1.722(4) Å in 9, 1.732(3) Å in 10, 1.734(8) Å in 13, 1.717(5) Å in 14, 1.740(5) Å in 15 and 1.732(4) Å in 16] confirm the presence of a triple bond Re-N imido . 18,19,22,23 Compared to the above mentioned [Re( p-NTol)X 2 (L)(PPh 3 )], the interatomic distances between the rhenium atom and the oxygen atom of phenolate-based ligands [1.972(3) 6599(3) b = 20.8513(6) b = 20.9641(6) b = 21.0563(4) b = 17.4480(4) c = 20.5169(6) c = 20.6190(7) c = 19.9772(5) c = 18.3654(5) β = 108.012(3 9) Å. 25 The Re-N(1) bond lengths in the [Re( p-NTol)X(L)-(PPh 3 ) 2 ] + of 7-10 and 13-16 well correlate with the values reported here for cis-(X,X)-[Re( p-NTol)X 2 (L)(PPh 3 )].…”