Mechanistic studies of phosphorus-oxygen bond cleavages in group 7 dinuclear complexes of 2-pyridyl dimethylphosphinite

Abstract

Dinuclear ~helatesfac-L~Re(CO)~[M(CO)~] (L2 = 2-pyridyl dimethylphosphinite, 2, M = Re; 3, M = Mn) rearranged in benzene at 80 OC to provide the corresponding (CO),Re(p-OPYR)(p-PMe,)M(C0)4 derivatives 5 (M = Re) and 6 (M = Mn) in 95 and 94% yield, respectively. The rearrangements exhibited first-order kinetics to >3 half-lives and displayed the following kinetic parameters: M = Re, AH* = 24.2 i 1.8 kcal/mol and pS* = -10 i 5 eu; M = Mn, AH* = 22.2 f 0.7 kcal/mol and AS" = -1 1 i 2 eu. The reaction rates and the products formed were unaffected by added CO, methylating agents, or triphenylphosphine. In the presence of carbon tetrachloride, the rearrangements afforded mixtures of the P-O cleavage products (5 or 6 ) andfac-(CO),L,ReCl. Crossover studies showed the rearrangements of 2 and 3 to occur with statistically significant inter-and intramolecular components. The results are discussed in light of mechanisms involving CO dissociation, homo-and heterolytic metal-metal bond cleavage, and a novel dyotropic rearrangement.Reports of the cleavage of phosphorus-carbon bonds by transition metals have received considerable attention recently because of their potential roles in the deactivation of homogeneous catalysts.' In contrast, the corresponding cleavages of phosphorusoxygen bonds in transition-metal phosphite complexes have been detailed on only a few occasions.2 Presumably this derives, in part, from the large ( 1 8 0 kcal/mol) P-0 bond e n e r g i e~.~ Nonetheless, we recently reported a notably facile cleavage of the P-0 bond of 2-pyridyl dimethylphosphinite (1) by CpCo-(CH2=CH2)2.4 In this paper we describe mechanistic studies of similar cleavages occurring on group 7 dinuclear frameworks. ResultsStarting Materials and Products. During studies of the chemistry of complexes of ligand 1,5 we prepared dinuclear complexes 2 and 3 as follows. Heating (C0)5ReBr6 with 1 .O equiv of ligand 1 in toluene for 15 min at 1 IO O C afforded fac isomeric complex 4 in an 88% yield after recrystallization. The fac stereochemistry was evident from the distinct resonances in the I3C and 'H NMR spectra of 4 for the diastereotopic methyl groups. When 4 was treated with NaRe(CO)S7 in T H F at 25 O C , dirhenium chelate 2 could be isolated in a 49% yield after recrystallization. Again, diastereotopic methyl resonances demonstrated the retention of the fac stereochemistry. The 3'P N M R spectrum of 2 showed a single resonance at 139.6 ppm. Heterodinuclear chelate 3 could be prepared in a 44% yield after recrystallization by treatment of 4 with (CO),MnNa8 in THF. The spectroscopic analysis of 3 proceeded analogously to 2. (9) Jones, R. A.; Wright, T. C.; Atwood, J. L.; Hunter, W. E. Organometallics 1983, 2, 470. Rosen, R. P.; Hoke, J. B.; Whittle, R. R.; Geoffroy, G. L.; Hutchinson, J. P.; Zubieta, J.Abstract The abstraction of benzylic hydrogen by bromine atom from toluene and 4-chlorotoluene has been studied by measuring the relative rates at 45.0,25.0 10.0, 0.0, -18.5, -32.0, and -50.0 "C. The rates of 3-chloro-, Cbrome, 4-methyl-, ...

Dyotropic Reactions: Mechanisms and Synthetic Applications

“…Collum and co-workers reported the rearrangement of dinuclear complexes 184, which upon heating at 80 °C in benzene rearrange to complexes 187 (Scheme 73). 125 It is proposed that dinuclear complexes 184 are in rapid equilibrium with complexes 185, which are able to undergo the type II dyotropic reaction, forming complexes 186. Complexes 186 finally afford the observed species 187.…”

Syntheses and reactions of .eta.5-(dimethylboryl)cyclopentadienyl cobalt and rhodium derivatives. Site-specific binding of unsaturated amines

“…[i)6-(py-Me2B )C5H4]Co(CO )2 (4). A glass bomb reactor was charged with a solution of Co2(CO)8 (12.8 g, 37.4 mmol) in CH2C12 (100 mL), triethylamine (4.8 g, 47.4 mmol), and 1 (8.75 g, 47.4 mmol).…”

“…NMR (200 MHz, C6D6) 8.39 (m, 2 H), 6.62 (m, 1 ), 6.30 (m, 2 H), 4.76 (dd, JHh = 1-9, 1.9 Hz, 2 H), 4.66 (dd, JHh = 1-9,1.9 Hz, 2 ), 0. ['?5-(py,Me2B)C5H4]Rh(CO)PPh3 (5).…”

“…NMR (400 MHz, CA) 7.77 (m, 2 ), 7.20-7.00 (m, 8 ), 5.60 (m, 1 ), 4.60 (d, JHH = 6.8 Hz, 1 ), 4.40 (m, 1 ), 4.19 (m, 1 ), 4.11 (m, 1 ), 2.19 (s, 3 ), 2.02 (dd, JHH = 12.5, 10.8 Hz, 1 ), 1.88 (dd, JHH = 12.5, 4.9 Hz, 1 ), 1.84 (s, 3 ), 0.98 (s, 1 ), 0.22 (s, 3 ), 0.00 (s, 3 ), -0.06 (ddd, JHH Found: C, 72.39; , 7.10.…”

“…eq l),1-3 attempts to prepare chelates of more reactive metals to achieve stereocontrolled functionalizations were thwarted by facile P-O1 234 and C-0 bond cleavages. [4][5][6] ocp "3% (1) We have turned to a new strategy that uses internal…”