Organic chemistry of dinuclear metal centres. Part 3. µ-Carbene complexes of iron and ruthenium from alkynes viaµ-vinyl cations

Abstract

Protonation of the complexes [M2(CO)(p-CO){p-C(0)C2R2)(q-C5H5)2] [M = Fe or Ru; R2 = H2, Ph, , H (Me), or H (Ph)] with H BF,*OEt, results in rapid carbon-carbon bond cleavage and formation of the p-vinyl cations [M2(CO)2(p-CO){p-C(R)=C(H)R)(q-C5H5)2] +, containing a cis arrangement of R groups. Addition of HBF,*OEt2 to [Ru,(CO) (p-CO){p-C(0)C2Me2}(q-C5H5)2] produces the cation [Ru2(CO) (p-CO)({p-C(H)(O)C,Me,)(q-C,H,),] +, which isomerises slowly to [ R u ~( C O ) ~( ~-C O ) { ~-C ( M ~) = C ( H ) M ~) ( ~-C ~H ~) ~]+. The p-vinyl cations exist in solution as isomers with cis and trans orientations of terminal ligands, shown by variable-temperature n.m.r. to interconvert ; cis isomers additionally display a fluxional oscillation of the p-vinyl ligand. Treatment of the cations with NaBH, yields p-carbene complexes [M2(CO)2(p-CO){p-C(R)CH2R)(q-C5H5)2] in good yield, also as cis and trans isomers which interconvert in solution. These result from hydride addition to the p-carbon of the p-vinyl, but addition to the or-carbon is apparent in the low-yield co-formation of the terminal ethylene complex [Ru2(C0)(p-CO),( C2H,) ( T ~-C ~H ~) ~] from the cation [Ru2(C0),(p-CO) (p-CH=CH2) (q-C5H5)2] +. Addition of sodium tetrahydroborate to [Ru,(CO)(p-CO){p-C( H)(0)C2Me2}(q-C5H5),] + provides the complex [Ru2(CO) (p-CO){p-C(Me)C(Me)CH2)(q-C5H5)2], completing a conversion of metallacyclic CO to CH2. Regeneration of the p-vinyl cation [M2(CO),(p-CO) (p-CH=CH2) ( T ~-C ~H ~) ~] + is achieved by treatment of [M2(C0),(p-CO){p-C( H) Me)(q-C5H5)2] with [CPh,] [BF,]. In Part 1 of this Series we reported the syntheses of di-iron Results and lX~u&On and diruthenium complexes [M2(CO)(p-CO)(p-C(0)C,R,>(rlp-Vinyl Cations.-Synthesis. Addition of HBF,*OEt2 to C5H5)2] (1)--(12) through reactions of alkynes with [M2(CO)4-an acetone or dichloromethane solution of the di-iron and (T)-C~H~)~].* The chemistry of these dimetallacyclopentenone diruthenium complexes [M2(CO)(p-CO){p-C(0)GR2)(q-hydrocarbon~.~*~ Aspects of this work have appeared as preliminary communications.6~' C5H&] (1)-(1 I ) results in immediate cleavage of the alkyne-CO link. The ' alkyne' portion of the dimetallacycle is protonated, generating p-vinyl cations [Mr(C0)2(p-CO)(p-CR'=C(H)R2}(q-C5H5)2][BF4] (1 3)--(23) in which R' and R2are cis to one another, while the metallacyclic ketonic carbonyl is transformed into a terminal ligand. Different behaviour is shown by the diruthenium complex (12), derived from but-2yne, which yields the appropriate p-vinyl cation (24) only very slowly and via a readily isolated intermediate ( 25). This anomaly is discussed in detail below. Infrared spectra indicated that the p-vinyl complexes are formed in clean,

A comparison between the reaction of P2Ph4 with [{Co2(CO)6}2(μ-η2:μ-η2-HOCH2CCCCCH2OH)] and the reaction of [Co2(μ-PPh2)2(CO)6] with HOCH2CCCCCH2OH

“…No coupling was resolved between the geminal vinyl protons. This correlates with other l-CR=CH 2 vinyl ligands for which negligible, or only a small coupling is observed [22][23][24][25][26][27][28]. The CH 2 protons of the lactone ring are observed as multiplets at d 4.32 and 4.18 with a geminal H-H coupling of 14 Hz and smaller unresolved coupling to both phosphorus atoms.…”

Stereochemistry of the insertion of disubstituted alkynes into the metal aminocarbyne bond in diiron complexes

“…Adams and Cotton put forward a mechanism for the cis-trans isomerization of [Fe 2 (l-CO) 2 (CO) 2 (Cp) 2 ] which is now a textbook example of the dynamic behaviour of metal carbonyl compounds [7] and cis-trans interconversion has been investigated in other related dinuclear complexes with lalkylidenes [8], l-CNR [9], and l-vinyl [10].…”

“…6, 133.5, 130.2, 129.9, 129.4 5H,Ph);5.76,5.43,5.01,4.39 (d,2H,2 J HH ¼ 15 Hz,CH 2 Ph);5.32,5.28,5.26,5.21 (s,10H,Cp); 4.14, 3.91, 3.86 (s, 6H, CO 2 Me); 3.77, 3.05 (s, 3H, NMe); (E:Z ratio ¼ 0.5). 13 Complex 12 has been obtained following the same procedure described for the synthesis of 10 .51 (s, 10H, Cp); 3.94 (t, 2H, 3 J HH ¼ 9 Hz, C c -CH 2 ); 3.85, 3.32 (s, 6H, NMe); 2.03 (m, 2H, C c -CH 2 CH 2 ); 1.92 (s, 3H, C b Me); 1.28 (t, 3H, 3 J HH ¼ 7 Hz, 3H, C c -CH 2 CH 2 CH 3 ). 13 C NMR (CDCl 3 ) d 255.1 (l-CO); 225.7 (C a ); 210.1 (CO); 201.9 (C c ); 90.4, 87.9 (Cp); 68.5 (C b ); 52.4 (C c -CH 2 ); 49.5,45.4 (NMe); 32.8 (C c -CH 2 CH 2 ); 14.7, 14.6 (C c -CH 2 CH 2 CH 3 and C b Me).…”

Reactivity of diosmacycles: complementary syntheses and structure Of [(µ-η1,η2-CHCH2)OS2(CO)8][BF4]

“…In particular, Knox and co-workers have shown that for complexes 4 the onset of vinyl oscillation for the iron complex is around 50°C, whereas the analagous ruthenium complex is static at this temperature (18). Following this trend, the lack of fluxionality of complex 3 is not that surprising.…”

“…Structure factor amplitudes are no longer being deposited and may be obtained directly from the author lation between two metal centers is well known (23) and renders numerous p-alkenyl complexes fluxional, the energetics of the process are both substituent (18, 19a) and metal dependent (18). In particular, Knox and co-workers have shown that for complexes 4 the onset of vinyl oscillation for the iron complex is around 50°C, whereas the analagous ruthenium complex is static at this temperature (18).…”