Regio- and stereoselective functionalization of cyclo-C-8 compounds by iterative nucleophilic and electrophilic addition to coordinated cyclooctatetraene

The addition of various nucleophiles (Nul) to the cationic complex [CpRu(et a(6)-cot)](+) (1(+)) has been performed and yielded the neutral complexes C pRu(eta(5)-C(8)H(8)Nu(1)) (2) [cot = cyclooctatetraene; Nu(1) = Me (2a), CH (CO2Me)(2) (2b), CH=CH2 (2c), C6H5 (2d), H (2e), D (2f), NMe2 (2g), OMe, (2 h), C=CtBu (2i)]. The nucleophiles Nu(1) add exclusively to the cot ring, a nd stereoselectively in the exo position with respect to the metal center. As evidenced by NMR spectroscopy the cyclo-Ce ligand in 2c, 2e-2i is bound in a 1,2-eta:5,6,7-eta fashion in solution. The molecular structure analysi s of 2e [space group P (1) over bar, a = 757.9(1), b = 759.1(1), c = 1053.1 (3) pm, alpha = 81.93(2), beta = 80.22(1), gamma = 88.73(1)degrees, V = 591 .1(2) Angstrom(3), Z = 2, R-merge = 0.0265] verifies the 1,2-eta:5,6,7-eta coordination mode of the cyclo-C-8 ligand in the solid state and shows the Nul substituent to be in an exo position. For 2a and 2b a 1,2,3,4,5-eta hap tomer is also found, and this interconverts to the 1,2-eta:5,6,7-eta deriva tive in solution; in contrast, the cyclo-C-8 ligand of the phenyl derivativ e 2d remains in the 1,2,3,4,5-eta fashion. The protonation of the neutral c omplexes 2a-2d by the addition of HBF, generates the new cationic products [CpRu(eta(6)-C(8)H(9)Nu(1))](+) (3(+)) [Nu(1) = Me (3a(+)), CH(CO2Me)(2) (3 b(+)), CH=CH2 (3c(+)), C6H5 (3d(+))]. When Nu(1) = CH(CO2Me)(2) (3b(+)) two different haptomers were isolated that exhibit 1,2-eta:4,5,6,7-eta and 1,2 ,3,4,5,6-eta bonding modes, respectively In solution the 1,2-eta:4,5,6,7-et a haptomer completely rearranges to the 1,2,3,4,5,6-eta derivative. The cry stal structure analysis of 3dBF(4) [space group Pbc2(1), a = 1678.8(7), b = 1031.4(1), c = 981.8(2) pm, V = 1700.0(9) Angstrom(3), Z = 4, R-merge = 0. 032] confirms the 1,2-eta:4,5,6,7-eta bonding mode of the cyclo-C8 ligand, which has also been indicated in solution. The second nucleophilic addition to the coordinated cyclo-C,:ligand yields new neutral complexes that exist as two different haptomers depending on the steric demand of the two nucle ophiles. The haptomer CpRu(1,2,3,4,5-eta-C8H9-6-Nu(1)-8-Nu(2)) (4a) is form ed with Nu(1) = Nu(2) = CH(CO2Me)(2) whereas with Nu(1) = Me, Nu(2) = CH(CO 2Me)(2) (4b) and Nu(1) = Nu(2) = Me (4c) the haptomer CpRu(1,2-eta:5,6,7-et a-C8H9-4-Nu(1)-8-Nu(2)) is obtained. The protonation of 4a-4c produces the cationic hydride species [CpRu(H)(1,2,3,4,5-eta-C(8)H(9)Nu(1)Nu(2))](+) (5( +)) [Nu(1) = Nu(2) = CH(CO2Me)(2) (5a(+)), Nu(1) = CH3, Nu(2) = CH(CO2Me)(2 ) (5b(+)), Nu(1) = Nu(2) = Me (5c(+))] as indicated by the high-field shift ed singlet for one proton below delta = -10 in the IH-NMR spectra. An X-ray structure analysis of a single crystal obtained from the protonation react ion of 4b [space group P2(1)/c, a = 1285.5(12), b = 1015.8(8), c = 1586.3(1 4) pm, beta = 108.61(7)degrees, V= 1963(3) Angstrom(3), Z = 4, R-merge = 0. 0942] reveals a special disorder, the interpretation of which results in th e structure determination of two independent complexes in a ratio of 59:41 differing by two hydrogen atoms in the formula. Both complexes are cations; one exhibits a disubstituted 1,2,3,4,5-eta-bonded cyclooctadienyl Ligand a nd an agostic interaction of the Ru center with a hydrogen atom at C5 of th e cyclo-C-8 ligand (5bBF(4)), whereas the second complex contains a cyclooc tatriene ligand in a 1,2,3,4,5,6-eta bonding mode without a metal hydride f unction (6BF(4)). The coexistence of two different molecules in one single crystal that differ by two hydrogen atoms in addition to the agostic hydrog en atom in 5b(+), points to an elimination of an Hz molecule from 5b(+) in the solid state to generate 6(+). This suggestion is corroborated by the fo rmation of a cationic complex 7(+) as the main product in solution, which c ontains a cyclo-C8 ligand without the malonate nucleophile [Nu(2) = CH(CO2M e)(2)], whereas a freshly prepared NMR sample only reveals 5b(+) and 6(+). In all of these products the Me nucleophile (Nu(1) = Me) is Linked to a met al-coordinated carbon atom indicating an additional intramolecular hydrogen migration after the initial protonation.