Chemistry of Fischer-type rhenacyclobutadiene complexes.: I.: Deprotonation, addition/substitution of nucleophilic reagents at α-carbon, and insertion of heteroatoms into rhenium-carbon bonds

The rhenacyclobutadienes (CO)(4)Re(eta(2)- C(R)C(CO2Me)C(OR')) (2) undergo a number of reactions that mirror those of Fischer alkoxycarbene complexes. Thus, (CO)(4)Re(eta(2)-C(Me)C(CO2Me)C(OEt)) (2a) can be deprotonated by LDA, Na[OBu-t], or Na[CH(CO2Me)(2)] to give the ylide-like conjugate base [(CO)(4)Re(eta(2)-C(=CH2)C(CO2Me)C(OEt)](-) (3), which was isolated as PPN(3). Li(3) undergoes deuteriation with DCl/D2O and alkylation with Et3OPF6 at ReC=CH2, with the latter reaction affording (CO)(4)Re(eta(2)-C(CH2Et)C(CO2Me)C(OEt)) (4). Repetition of the sequence deprotonation-ethylation on 4 generates (CO)(4)Re(eta(2)-C(CHEt2)C(CO2Me)C(OEt)) (5). The nature of the alkoxy substituent in 2 can be varied by use of the rhena-cyclobutenones Na[(CO)(4)Re(eta(2)-C(R)C(CO2Me)C(O))] (Na(1)) in conjunction with AcCl and R'OH to produce a series of new complexes (R = Ph, R' = Et (2b); R = Me. R' = CH2CH=CH2 (2c), (CH2)(3)Cequivalent toCH (2d), Me (2e)). Aminolysis of 2a with the primary and secondary amines PhNH2, HO(CH2)(2)NH, p-TolNH(2), and Et2NH yields the aminorhenacyclobutadiene complexes NR2')) (R-2'=Et-2 (6a); R`= Ph (6b), (CH2)(2)OH (6c), p-Tol (6d)). These complexes (CO)(4)Re(eta(2) - C(Me)C(CO2Me)QNHR' or display lesser carbene-like character than their alkoxy counterparts 2, as evidenced by H-1 and C-13 NMR spectroscopic properties and lack of reactivity toward LDA by 6a. Reactions of each 2a and 6a with PPhMe2 at low temperature afford (CO)(4)Re(eta(2)-C(Me)(PPhMe2)C(CO2Me)C(OEt)) (7) and (CO)(3)(PPhMe2)Re(eta(2)-C(Me)C(CO2Me)C(NEt2)) (9), respectively. further in agreement with the more carbenoid nature of 2a than 6a. 7 undergoes conversion to (CO)(3)(PPhMe2)Re(eta(2)-C(Me) C(CO2Me)C(OEt)) (8) upon heating. 2a reacts with each of (NH4)(2)[Ce(NO3)(6)], DMSO, EtNO2/Et3N, and Me3NO under various conditions to afford one or both of the oxygen atom insertion products into the Re=C bonds. (CO)(4)Re(kappa(2)-OC (Me)C(CO2Me)C(OEt)) (10) and (CO)(4)Re(kappa(2)-C(Me)C(CO2Me)C(OEt)O] (11). In contrast, no reaction occurred between 2a and S-s on heating. However, 6a was converted to the NH insertion product (CO)(4)Re(kappa(2)-NHC(Me)C(CO2Me)C(NEt2)] (12) by the action of H2NNH2 (.) H2O at 0 degreesC. All new compounds were characterized by a combination of elemental analysis, mass spectrometry. and IR and NMR spectroscopy. (C) 2004 Elsevier B.V. All rights reserved.