Synthesis and transformations of 60-, 62-, and 64-electron Co₄(CO)_x(PNR₂)₂(x= 8, 9, 10) clusters

Abstract

A unique family of bis-(amino)phosphinidene Co 4 clusters with electron counts in the 60-64 e regime is described. The 62-electron (5 Co-Co) butterfly compound [Co 4 (CO) 8 (µ-CO){µ 3 -P(TMP)} 2 ] (TMP = 2,2,6,6-tetramethylpiperidyl) (1a) is obtained via condensation of the bridged (amino)phosphinidene complex [Co 2 (CO) 6 {µ-P(TMP)}]. Further heating and removal of CO gives the 60-electron (6 Co-Co) tetrahedral compound [Co 4 (CO) 6 (µ-CO) 2 {µ 3 -P(TMP)} 2 ] (3a). The reaction of K[Co(CO) 4 ] with PCl 2 (N-i-Pr 2 ) gives the 64-electron (4 Co-Co) square-planar derivative [Co 4 (CO) 8 (µ-CO) 2 (µ 4 -PN-i-Pr 2 ) 2 ] (2), which loses one carbonyl ligand to form the 62-electron (5 Co-Co) butterfly compound [Co 4 (CO) 8 (µ-CO)(µ 3 -PN-i-Pr 2 ) 2 ] (1b). Complex 1b releases another carbonyl to form the 60-electron (6 Co-Co) tetrahedral compound [Co 4 (CO) 6 (µ-CO) 2 (µ 3 -PN-i-Pr 2 ) 2 ] (3b). X-ray structural analyses of compounds 1a, 1b, 2, and 3a have been carried out. The reversibility of the CO elimination reactions and the structural rearrangements accompanying changes in electron count in this series are discussed. Résumé :On décrit une famille unique d'agrégats de la famille du bis-(amino)phosphinidène Co 4 comportant de 60 à 64 électrons. Le composé en forme de papille comportant 62 électrons (5 Co-Co), le [Co 4 (CO) 8 (µ-CO){µ 3 -P(TMP)} 2 ] (TMP = 2,2,6,6-tétraméthylpipéridyl) (1a) est obtenu par condensation du complexe (amino)phosphinidène ponté [Co 2 (CO) 6 {µ-P(TMP)}]. Un chauffage additionnel avec élimination du CO conduit au composé tétraédrique à 60 élec-trons (6 Co-Co) [Co 4 (CO) 6 (µ-CO) 2 {µ 3 -P(TMP)} 2 ] (3a). La réaction du K[Co(CO) 4 ] avec le PCl 2 (N-i-Pr 2 ) 2 conduit au dérivé plan carré à 64 électrons (4 Co-Co) [Co 4 (CO) 8 (µ-CO) 2 (µ 4 -PN-i-Pr 2 ) 2 ] (2) qui perd un ligand carbonyle pour former le composé en forme de papillon comportant 62 électrons (5 Co-Co), le [Co 4 (CO) 8 (µ-CO)(µ 3 -PN-i-Pr 2 ) 2 ] (1b). Le composé 1b perd un autre ligand carbonyle pour former le composé tétraédrique à 60 électrons (6 Co-Co) [Co 4 (CO) 6 (µ-CO) 2 (µ 3 -PN-i-Pr 2 ) 2 ] (3b). On a déterminé les structures des composés 1a, 1b, 2 et 3a par diffraction des rayons X. On discute de la réversibilité des réactions d'élimination du CO et des réarrangements de structure qui accompagnent les changements dans les nombres d'électrons dans ces séries.

Phosphinidene-bridged binuclear complexes

“…The influence of the metal in these reactions was also notable, since analogous reactions with [HfCl 2 Cp 2 ] failed to yield any phosphinidene complex [25], while reaction of [WCl 2 Cp 2 ] with Li[(SiMe 3 )P-P i Pr 2 ] yielded the cyclopentadienylidene-phosphinidene complex [W 2 Cp 2 (μ-κ 1 :κ 1 ,η 5 -A similar silyl redistribution process following the salt metathesis step has been invoked by Chen and co-workers to explain the formation of the neodymium bis(phosphinidene) complex (17) in the reaction of [NdI 3 (THF) 3.5 ] with K[P(SiMe 3 )(DIPP)] (DIPP = 2,6-i Pr 2 C 6 H 3 ; Scheme 9) [27]. This paramagnetic compound could be characterised in the solid state and exhibits two phosphinidene ligands with an almost perfectly trigonal planar geometry around the P atoms.…”

“…Thus, reaction of K[Co(CO) 4 ] with Cl 2 PR (R = TMP, N i Pr 2 ) at low temperature led to the unstable phosphinidene complexes [Co 2 (μ-PR)(CO) 6 ] (R = TMP [16], N i Pr 2 [17]), which at room temperature evolved rapidly by CO loss to generate different clusters. Fortunately, more stable derivatives of formula [Co 2 (μ-PR)(μ-κ 1 :κ 1 -dppm)(CO) 6 ] (R = TMP(8a) [16], N i Pr 2 (8b) [18]; dppm = Ph 2 PCH 2 PPh 2 ) were prepared when these reactions were carried out in the presence of the dppm ligand.…”

“…In the absence of an stabilising ligand (such as dppm), the dicobalt aminophosphinidene complex [Co 2 (CO) 6 {μ-P(TMP)}] loses CO in hexane solution to yield the tetracobalt cluster 177 (Scheme 87), whose formation can be rationalised as resulting from condensation of two [Co 2 (CO) 6 {μ-P(TMP)}] molecules with loss of three CO ligands [17]. The structure of the latter was confirmed by an X-ray diffraction analysis, evidencing the presence of two μ 3 -phosphinidene ligands, in good agreement with the 31 P NMR spectrum of the complex, which displays two broad low-field resonances at 542 and 472 ppm, respectively.…”

Reactivity of electrophilic µ-phosphinidene complexes with heterocumulenes: formation of the first σ-π-aminophosphaimine complexes [Mn2(CO)8{µ-η1,η2-P(NiPr2)NR}] and diazoalkane insertions into metal–phosphorus bonds

“…6 Although bridging carbenes (m-alkylidenes) 7 comprise an important and diverse class of organometallic molecules and intermediates, their m-PX counterparts are relatively rare and their chemistry is virtually unexplored. 8,9 There are also structural and electronic differences between m-CX 2 and m-PX complexes: whereas bridging carbenes are formally saturated with tetrahedral stereochemistry at carbon as in I, in the latter, II, the phosphorus centre is planar and unsaturated, 10 and reactivity may be initiated by attack at the electrophilic phosphorus atom.…”

“…This compound is surprisingly stable and persists for days in THF solution, whereas the related complexes [Co 2 (CO) 6 (m-CO)(m-PNR 2 )] (NR 2 5 N i Pr 2 , TMP) readily lose carbonyl ligands and undergo condensation reactions to form the cluster complexes [Co 4 (CO) 8 (m-CO){m 3 -PNR 2 } 2 ] (NR 2 5 TMP, N i Pr 2 ). 8 Complex 1 has a 31 P NMR resonance at d 731, the downfield chemical shift of which is typical for bridging phosphinidene ligands. 8 The X-ray structure{ shows a pseudooctahedral ligand arrangement about each manganese centre and a bridging aminophosphinidene ligand across the two metal centres (Mn(1)-Mn(2) 5 2.9193(4) A ˚).…”