Superamidines 2. Synthesis of the bulky ligand N,N'-bis-(2,6-diisopropylphenyl)-trifluoroacetamidine and its molybdenum carbonyl complex

Abstract

N,N'-bis-(2,6-diisopropylphenyl)trifluoroacetamidine has been prepared for the first time from 2,6-diisopropylaniline and the trifluoroacylation reagent TFAP via the imidoylchloride. The crystal structure of the amidine was determined, indicating that it crystallizes in the Z-anti tautomer, in contrast to the nonfluorinated analogue, which is E-anti in the solid state. In solution, as indicated by NMR spectroscopy, it exists in two isomeric forms. The amidine reacts with Mo(CO)6 to produce a coordination complex with Mo(CO)3 in which the ligand is also in the Z-anti geometry, the metal is η6-coordinated to the imino-2,6-diisopropylphenyl ring, and the amino N-H unit is directed towards the metal, as determined by a single-crystal X-ray structure. Unlike the analogous nonfluorinated acetamidine, there is no indication of an intermediate in which the neutral amidine is coordinated in a monodentate fashion to an Mo(CO)5 unit, which we now attribute to the predominant geometry of the ligand, both in the solid state and in solution, being Z-anti. The high steric bulk of this superamidine ligand apparently prevents the formation of a metal-metal bonded Mo2(amidinate)4 as observed previously in a redox reaction between N,N'-diphenylbenzamidine and Mo(CO)6 under similar thermal reaction conditions.Key words: trifluoromethyl, superamidine, amidine, molybdenum, carbonyl, coordination.

Extremely bulky triarylphosphines incorporating 2,6-diisopropylphenyl substituents; consideration of steric shielding and steric pressure

“…Similarly, since our report on the bulky guanidine (E = N,N,N) [10], there have been several other reports on bulky guanidine and guanidinate derivatives. We have demonstrated that the presence of these bulky groups -which are completely unnecessary to stabilize the organonitrogen architectures -induces significant differences in the structure and chemical behaviour of these functional groups in comparison to small organic substituents [6,10].…”

“…Since our initial work on what at the time were the bulkiest amidines to have been reported [6], there has been an explosion of interest in the chemistry of amidines and their deprotonated amidinate congeners [8], coinciding with the fascinating reports from Jordan on alkene polymerization using dimethylaluminium derivatives of amidines which operate without the addition of any transition metals [9]. Similarly, since our report on the bulky guanidine (E = N,N,N) [10], there have been several other reports on bulky guanidine and guanidinate derivatives. We have demonstrated that the presence of these bulky groups -which are completely unnecessary to stabilize the organonitrogen architectures -induces significant differences in the structure and chemical behaviour of these functional groups in comparison to small organic substituents [6,10].…”

Hetarylamidines derived from PtIV-mediated coupling of nitriles with aminoheterocycles

“…This reaction most often produces amidinate complexes 2,6-8 and much more rarely affords nondeprotonated amidine metal derivatives. 1, [9][10][11][12][13] An other approach to the synthesis of amidine complexes is based on the nucleophilic addition of various NH con taining compounds (for example, of primary or secondary amines, diamines, aziridine, amino alcohols, or amino acid esters 14-17 ) to coordinated nitriles or generation of amidine ligands in the metal mediated transformations involving the above mentioned amino containing nucleo philes in nitrile media. These reactions readily proceed if nitrile substrates are coordinated to metal centers, such as Co III , 18 Cu I , 19 Rh III , 20 W II , 21 Re IV , 22 Ir I , 23 Pt II , or Pt IV .…”

Short Intramolecular N–H⋯C(carbonyl) Interactions in Mixed-Ligand Molybdenum Hexacarbonyl Derivatives

“…The systematic absences uniquely identified the space group as P2 1 /n (No. 14) in each case and the structures were solved by direct methods with SHELXS and the atomic models refined against F 2 with SHELXL [20]. The "observed data" threshold for calculating the R(F) residuals was set as I > 2(I).…”