Transition Metal Nitrosyls: Statistics, Charge Estimates via CDVR, and Studies of Tetradentate Chelate Diamides (pddi)M and (pddi)MNO (M = Cr, Fe, and Co)

The dn Number in Transition Metal Chemistry: Its Utility and Limitations

“…For a recent paper which considers how to estimate charge distribution in metal nitrosyl complexes, see ref. [67] and for a discussion of the factors which affect the linear vs. bent (or intermediate) geometries in the cationic species [MCl(NO) 2 (PPh 3 ) 2 ] + (M = Ru, Os), see ref. [68].…”

“…As a result, Enemark and Feltham proposed the {MNO} n notation (cited earlier) where the value of n is the d n number of the complex when the NO ligands are treated as NO + [48,49] (Appendix A Note 16). Nevertheless, the NO + /NO − classification remains a topic of continued interest, as demonstrated in the recent publications by Klüfers et al concerning whether or not a range of {CoNO} 8 complexes should be classified as Co(III)-NO − or Co(I)-NO + [61,62] (Appendix A Note 21) [63][64][65][66][67][68].…”

Reduction of (pddi)Cr reveals redox noninnocence via C–C bond formation amidst competing electrophilicity: [(cpta)CrMen]− (n = 0, 1) and [(pta)Cr]−

“…Redox noninnocence (RNI) is a means of expanding the oxidative addition/reductive elimination capability of metal complexes via the shuttling of electrons in and out of peripheral ligands. 1–7 Previously, these laboratories explored the concept of redox noninnocence in (pddi)Cr (pddi 2− = [Me 2 C{CHN(1,2-C 6 H 4 )N(2,6- i Pr 2 C 6 H 3 ) 2 }] 2− ) 8 via cyclopropane C–C bond formation in the ligand backbone. 9–12 Anticipated nitrosylation products containing (cpta)Cr m (cpta n = [2-Me 2 C 3 H 2 {1,2- N (1,2-C 6 H 4 )N(2,6- i Pr 2 C 6 H 3 ) 2 }] 4− ) were unrealized, prompting the design of more direct approaches.…”

“…The [(cpta)Cr] anion in 2c is separate from the [K(18-c-6)(THF) 2 ] cation, and its metrics are clearly those of a tetraamide. Chromium–nitrogen bonds to the imine in 1 ( S = 2) average 2.076(9) Å, 8 while the corresponding amide linkages in 2c average 1.9401(6) Å, and all of its CrN bond distances are shorter in concert with the change from Cr( ii ) to Cr( iii ). 14 The cyclopropane C–N single bond lengths are 1.4316(6) (ave) Å while the related imine distances are 1.289(4) (ave) Å, 15 and the new C–C bond is 1.509(2) Å, a distance whose bond enthalpy is about 101(2) kcal mol −1 .…”

“…Chromium–nitrogen bond distances listed in the caption are consistent with amide linkages, and the backbone CC- and CN-distances possess C(sp 3 )–C(sp 3 ), and the N–C(sp 3 ) values. 15 The pseudo square-planar coordination manifests greater distortion (Σ ∠NCrN = 375.9°) than 1 (360.8°), 8 2c (360.7°), and 4 (362.9°), presumably due to the tetraamide core in combination with the added sterics of the anti-arrangement of the benzylated backbone.…”