Oxygen-atom transfer from nitrous oxide. Identification of intermediates in the oxidation of diphenylacetylene at Group 4 metal centers and the structural characterization of (.eta.-C5Me5)2Ti{N(O)NCPh:CPh}.cntdot.1/2C7H8

Functionalization of Complexed N2O in Bis(pentamethylcyclopentadienyl) Systems of Zirconium and Titanium

“…11 The only significant perturbation is the Ti–N(1) bond distance of 2.185(4) Å, which reflects slight elongation from that of its neutral counterpart (Figure 4). Table 2 lists selected metrical parameters for Cp* 2 Ti(N(O)NCPhCPh) 11 and the radical anion core of 5 .…”

“…11 Upon generation of metastable Cp* 2 Zr(N(O)NCPhCPh), we found that addition of a cold toluene solution of MeO 3 SCF 3 (−78 °C) rapidly results in formation of the orange salt [Cp* 2 Zr(N(O)N(Me)CPhCPh)][O 3 SCF 3 ] ( 1 ) in 48% isolated yield (Scheme 3). The ionic nature of 1 allows for facile separation from the reaction mixture, and, unlike its predecessor Cp* 2 Zr(N(O)NCPhCPh), compound 1 is relatively stable as a solid when stored at −35 °C.…”

“… 47 All optimizations were performed with C 1 symmetry, and all minima were confirmed by analytical calculation of frequencies, which were also used to compute zero point energy corrections without scaling. The initial geometry of Cp 2 Ti(N(O)NCMeCMe) and Cp 2 Zr(N(O)NCMeCMe) was adapted from a refined crystal structure of (Cp*) 2 Ti(N(O)NCPhCPh) 11 with all methyl groups on the Cp* replaced with H and phenyl groups on the metallacycle replaced by methyls.…”

“… 3 − 21 Unfortunately, and as noted before, this molecule is kinetically inert due to its poor properties as a ligand, 22 − 24 consequently resulting in only a handful of systems being capable of complexing N 2 O without the entropic and enthalpic driving force to N 2 ejection and metal oxo formation. 11 , 12 , 18 , 22 − 31 Thus, the use of N 2 O as an oxidizing substrate in transition metal chemistry is often hampered by a combination of kinetic inertness and inevitable oxidation of the metal center, concomitant with entropy-assisted loss of a thermodynamically stable molecule such as dinitrogen. 32 …”

“… 12 The fact that the azoxymetallacycle complex Cp* 2 Ti(N(O)NCPhCPh) 11 , 12 , 33 was not prone to dinitrogen elimination under ambient conditions (unlike its Zr derivative), to give a hypothetical oxametallacyclobutene system Cp* 2 Ti(OCPhCPh), led us to speculate that such a system could be ideal for O atom and/or functionalization reactions stemming from N 2 O complexation (Scheme 1 ). 11 In addition, the azoxymetallacyclobutene moiety in complexes of the type Cp* 2 M(N(O)NCPhCPh) (M = Ti or Zr) provides an ideal opportunity to examine the charge distribution about this rare functionality since several canonical forms can be envisioned (Scheme 2 ). While resonance structures A and B represent zwitterionic forms with negative charge being localized on β-O and the β-N, respectively, resonance form C can be best represented as an ylide, having more nucleophilic character on O (Scheme 2 ).…”