Synthesis of [Co₂(µ-PPh₂C₃H₄)(µ-PPh₂)(CO)₄]; its reactions with P(OMe)₃and with alkynes

Abstract

The bis(phosphid0) -bridged complex [Co,(p-PPh,),(CO),] 1 undergoes an insertion reaction of allene into one of the phosphido bridges, to give the new ligand-bridged dinuclear cobalt complex [Co,(p-PPh,C,H,)(p-PPh,) (CO),] 2 in high yield. Complex 2 reacts with P(OMe), to give the monosubstituted derivative [Co,(p-PPh,C,H,) (p-PPh,) (CO),{P(OMe),}] 3 in which substitution has occurred at the allyl-co-ordinated cobalt atom. Complex 2 also reacts with alkynes, RCECH (R=CH,OH, Me or H), which insert into the remaining phosphido bridge along with a molecule of CO to give [Co,(p-PPh,C,H,){p-PPh,C(O)CHCR}(CO),] (R = CH,OH 4a. Me 4b or H 4c). In the case of MeCSCH which gives 4b. a second isomer, [CO,(~-PP~,C,H,){~-PP~,C(O)CM~CH}(CO)~] 5, which differs in the mode of insertion of the alkyne, is also obtained. The isomeric complexes [Co,(p-PPh,C(O)CHCR}(p-PPh,)(CO),] ( R = CH,OH 6a or Me 6b) and [CO,(~-PP~,C(O)CRCH}(~-PP~,)(CO),] (R = CH,OH 7a or M e 7b), which may be regarded respectively as analogues of 4 and 5 but with a phosphido bridge and an additional terminal CO group in place of the p-PPh,C,H, ligand, have been prepared from [Co,(p-RCCH)(CO),] (R = CH,OH or Me) and P,Ph,. The complexes [Co,(p-PPh,CHCRC(O)}(p-PPh,)(CO),](R = CH,OH 8a or M e 8b). which are also isomers of complexes 6a. 7a and 6b. 7b respectively, have also been obtained in these latter reactions. The complexes 8 contain a bridging ligand which differs from that present in 6 and 7 in that t h e ordering of the PPh,, alkene and CO components of the bridging ligand is not the same. The crystal structures of the complexes 3 and 4c have been determined by X-ray diffraction studies.The insertion of alkynes into the metal-phosphorus bonds of phosphido-bridged dinuclear complexes is more common than originally thought and usually gives new dinuclear complexes with a bridging ligand derived from one phosphido group, one molecule of alkyne and sometimes also a CO or -C=CR group if these are present in the original complex. '-*Starting from the bis(phosphid0)-bridged complex [Co,-(p-PPh,),(CO),] 1, we recently reported the stepwise synthesis of the complexes [Co,{ p-PPh,CR'=CR2C(0)CR3=CR4-PPh2}(C0),] (R = H, alkyl, aryl, C0,Me or silyl).' These complexes each contain a bridging nine-membered dimetallacyclic ring formed from the coupling of both phosphido groups in 1 with two alkyne molecules and one CO molecule. In the light of this ability of [Co,(p~-PPh~)~(C0)~1 1 to undergo alkyne insertions to give novel ligand-bridged species we decided to explore its reactivity with allene.In this paper we present a study of the reaction of 1 with allene and of the reactivity of the product, [Co,(p-PPh,C,H,)-(p-PPh,)(CO),] 2, towards P(OMe), and alkynes (Scheme 1). The reactions of 2 with alkynes, R C S H , gives the alkyneinserted products [Co2(p-PPh2C3H,){p-PPh2C(0)CHCR)-(CO),] (R = CH,OH 4a, Me 4b or H 4c) and [Co,(p-PPh,-C,H,){ p-PPh,C(O)CRCH)(CO),] (R = Me 5). For comparative purposes the five-membered metallacyclic ring-containing complexes [Co, { p-PPh,C(O)CHCR}...

Reactions of a phosphido-bridged unsymmetrical diiron complex (η5-C5Me5)Fe2(CO)4(μ-CO)(μ-PPh2) with various alkynes

“…The first step is most probably the coordination of the alkyne to the iron atom without a bulky g 5 -C 5 Me 5 ligand with either metal-metal bond cleavage or CO loss to give intermediates C or D. Then, the coupling of a carbonyl group and the alkyne in C or D affords 3 or the intermediate E, respectively. An intermediate related to E involving a five-membered M-CR@CR 0 AC(O)AM metallacyclic ring has been previously proposed in the reaction of Co 2 (l-HCBCH)(CO) 6 with P 2 Ph 4 to give Co 2 [l-HX@CHC(O)PPh 2 ](l-PPh 2 )](CO) 4 [26]. A CO loss from E leads to the formation of 3 in the case of t BuCBCH.…”

Deprotonation of [Mo(COMe)(CO)2(PPh2H)(η-C5H5)] and reaction with activated alkynes: controllable formation of vinylphosphine and η3-acryloyl ligands

“…2 The assembly of a similar five-membered ring from an alkyne, a CO ligand and a phosphido group has also been reported at a dicobalt centre by Mays and co-workers. 14…”

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

“…Cobalt carbonyl complexes containing phosphorus-donor ligands are amongst the most active in reactions of this type [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The study of P-C and PCo bond cleavage and formation in these complexes provides an insight into aspects of the chemistry of cobalt carbonyl phosphine hydroformylation catalysts [21].…”

“…15)-C(16) 1.491(6) O(16)-C(16) 1.433(5)P(1)-Co(1)-Co(2) 87.50(4) P(2)-Co(2)-Co(1) 87.45(4) Co(1)-P(1)-P(2) 92.03(6) Co(2)-P(2)-P(1) 92.43(6) O(11)-C(11)-C(12) 112.2(4) C(13)-C(12)-C(11) 133.6(4) C(12)-C(13)-C(14) 139.7(4) C(15)-C(14)-C(13) 142.0(4) C(14)-C(15)-C(16) 140.5(4) O(16)-C(16)-C(15) 109.4(4) the structure of 1 and of [Co 2 (l-P 2 Ph 4 ){l-g 2 -C 2 (CO 2 Me) 2 }(CO) 4 ] in which the Co-P-P-Co atoms are planar and the Ph rings are eclipsed. Fully eclipsed, fully staggered and intermediate conformations of P 2 Ph 4 ligands have been reported at different metal centers [1,46-54].…”