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DOI: 10.1039/A804025G (Paper) Reference Section for: J. Chem. Soc., Dalton Trans., 1998, 2281-2284

Mimicking the binding of glutamate to zinc in thermolysin and carboxypeptidase: the synthesis of [η3-(HCO2)BpBut,Pri]ZnCl by insertion of CO2 into a B–H bond of the bis(pyrazolyl)hydroborato zinc complex [BpBut,Pri]ZnCl

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Prasenjit Ghosh and Gerard Parkin

Abstract

Insertion of CO2 into one of the B–H bonds of the bis(pyrazolyl)hydroborato complex [BpBut,Pr[hair space]i[hair space]]ZnCl yields [η3-(HCO2)BpBut,Pr[hair space]i[hair space]]ZnCl; the carboxylate group of the generated [NNO] donor ligand mimics the glutamate residues at the active sites of thermolysin and carboxypeptidase.

References

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  15. A solution of [BpBut,Pri]ZnCl (0.25 g, 0.56 mmol) in C6H6(ca. 10 mL) in an ampoule was treated with CO2[ca. 2 atm (1 atm = 101 325 Pa)] and stirred overnight at 50 °C. The volatile components were removed in vacuo and the residue was washed with pentane (5 mL) to give [η3-(HCO2)BpBut,Pri]ZnCl as a white solid (0.16 g, 59%)(Found: C, 51.9; H, 7.5; N, 11.6. Calc. for C21H36BClN4O2Zn: C, 51.7; H, 7.4; N, 11.5%). IR data (cm–1, KBr pellet): 2586 [ν(B–H)], 1650 and 1336 [ν(C–O)]. 1H NMR, (C6D6): δ 1.07 [d, 3JH–H= 7, 6 H, CH(CH3)2], 1.19 [d, 3JH–H= 7, 6 H, CH(CH3)2], 3.33 [sept, 3JH–H= 7, 2 H, CH(CH3)2], 1.54 [s, 18 H, C(CH3)3], 5.98 [s, 2 H, C3N2H], 7.21 [s, 1 H, HCO2], BH not located. 13C NMR (C6D6): δ 22.4 [q, 1JC–H= 127, 2 C, CH(CH3)2], 23.4 [q, 1JC–H= 127, 2 C, CH(CH3)2], 26.9 [d, 1JC–H= 129, 2 C, CH(CH3)2], 30.8 [q, 1JC–H= 126, 6 C, C(CH3)3], 32.2 [s, 2 C, C(CH3)3], 100.5 [d, 1JC–H= 175, 2 C, C3N2H], 158.9 [s, 2 C, C3N2H], 165.0 [s, 2 C, C3N2H], 168.2 [d, 1JC–H= 224 Hz, 1 C, HCO2]..
  16. Coupling in the 1H NMR spectrum was observed using enriched 13CO2.
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  18. [η3-(HCO2)BpBut,Pri]ZnCl: C21H36BClN4O2Zn, triclinic, P[1 with combining macron](no. 2), a= 9.800(3), b= 9.856(4), c= 13.742(3)Å, α= 74.87(3), β= 83.04(2), γ= 83.95(3)°, U= 1268.1(7)Å3, Z= 2, µ= 1.096 mm–1, T= 293(2) K, R1 = 0.0558 for 3224 reflections. CCDC reference number 186/1038.
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  24. The first report of CO2 insertion into a B–H bond of which we are aware involves the reaction of NaBH4 with CO2 to give, depending upon conditions, Nax[BO(OCH3)(O2CH)]x and Na[HB(O2CH)3].24a However, these compounds were neither spectroscopically nor structurally authenticated. More recently, [(biL)(Ph3P)Cu][BH4] was reported to react with CO2 in the presence of PPh3 to give [(biL)(Ph3P)2Cu][HB(O2CH)3] and [(biL)(Ph3P)2Cu][H2B(O2CH)2](biL = 1,10-phenanthroline and 3,4,7,8-tetramethyl-1, 10-phenanthroline), which were spectroscopically characterized.24b (a) T. Wartik and R. K. Pearson, J. Inorg. Nucl. Chem., 1958, 7, 404 CrossRef CAS; (b) G. L. Monica, G. A. Ardizzoia, F. Cariati, S. Cenini and M. Pizzotti, Inorg. Chem., 1985, 24, 3920 CrossRef.
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