Coinage metal complexes of the carbenic tautomer of Nitron

Iron and Cobalt Metallotropism in Remote‐Substituted NHC Ligands: Metalation to Abnormal NHC Complexes or NHC Ring Opening

“…[4] Competition between the C NHC and r(substituent) sites for metal coordination is sterically and electronically tunable. [3a] Tautomeric equilibria involving the C NHC basic site and the r(substituent), altering the nature and electronic characteristics of the donors,c an lead to increased bonding diversity (compare equilibria involving Nitron, recently extended to its alkyl analogues [5] and other mesomeric betaines [6] ). With 1,3-bis-(DiPP)imidazolium systems (DiPP = diisopropylphenyl), the tautomerism between the imidazolium aminide (IA)( with anionic r(N exo R)) and the amino carbene (AC)( with neutral r(NHR)) depends on the nature of R: aromatic and tBu substituents favor the IA and AC forms,r espectively (Scheme 1).…”

Coinage Metal Complexes of the Carbenic Tautomer of a Conjugated Mesomeric Betaine Akin to Nitron

“…Related work on other five-membered CMBs in equilibrium with their tautomeric NHCs was published by the groups of César and Lavigne [ 35 , 36 , 37 ], Braunstein and Danopoulos [ 38 , 39 , 40 ], Ganter [ 41 ] and Schmidt [ 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ], who also provided the first review of this burgeoning field [ 50 ]. We demonstrated that the electronic properties of 2 ′ are very similar to those of the “Enders carbene” ( 1 ) [ 31 , 32 , 33 ], as is reflected by their essentially identical Tolman Electronic Parameter (TEP) values [ 51 ] as well as by the very similar 77 Se NMR chemical shift values (∆δ = 4 ppm) determined for their corresponding selenone derivatives. In our present work we describe a homologue containing N -alkyl substituents instead of the N -phenyl substituents present in 2 ′.…”

“…We recently described the use of the analytical reagent Nitron ( 2 ; Figure 1 ) as an “instant carbene” [ 31 , 32 , 33 ], whose reaction with coinage metal salts MX in dipolar aprotic solvents afforded complexes of its carbenic tautomer 1,4-diphenyl-3-phenylamino-1,2,4-triazol-5-ylidene ( 2 ′; Figure 1 ) under mild conditions [ 33 ]. With a stoichiometric ratio of 1:1 complexes of the type [MX( 2 ′)] were obtained; a stoichiometric ratio of 2:1 furnished complexes of the type [MX( 2 ′) 2 ] or [M( 2 ′) 2 ]X.…”

“…A comparison of the HOMO energies and singlet-triplet gaps of 1 and its methyl homologue 1,3,4-trimethyl-1,2,4-triazol-5-ylidene ( 3 ; Figure 1 ) indicates that alkyl homologues of 1 are comparatively more nucleophilic and less electrophilic [ 52 ]. Although experimental evidence in support of these computational results is not available for the particular pair 1 and 3 , the data obtained for corresponding derivatives of 1 and 1,4-dimethyl-1,2,4-triazol-5-ylidene ( 4 ; Figure 1 ) clearly show that the alkyl-substituted NHC is less electrophilic (δ( 77 Se): 20 vs. 110 ppm for the respective selenone derivative [ 53 ] 4 = Se [ 54 ] and 1 = Se [ 33 ]) and has a higher net electron donor capacity than 1 (TEP value according to the linear regression given by Dröge and Glorius [ 55 ]: 2054 [ 56 ] vs. 2057 cm −1 [ 57 ] for 4 and 1 , respectively). Similar effects may plausibly be expected for alkyl homologues of 2 ′.…”

Crystal structure of (1,4-diphenyl-4H-1,2,4-triazol-3-yl)phenylamine difluorophosphate, and a survey of the difluorophosphate anion (PO2F2 −)

“…Nitron has been utilized as a reagent for gravimetric analysis of the nitrate anion ('Busch's reagent'; Busch, 1905) from slightly acidic solutions under formation of the salt C 20 H 17 N 4 + ÁNO 3 À . In recent years, inexpensive Nitron was rediscovered as a stable N-heterocyclic carbene (Fä rber et al, 2012) that can be reacted with several coinage or other noble metals to yield corresponding metal complexes (Hitzel et al, 2014;Thie et al, 2016). The Nitron salt of difluorophosphoric acid, C 20 H 17 N 4 + ÁPO 2 F 2 À (III) was reported by Lange more than 90…”