Coordination Behavior of a P4 -Butterfly Complex towards Transition Metal Lewis Acids: Preservation versus Rearrangement

Low-oxidation state cobalt-magnesium complexes: ion-pairing and reactivity

Magnesium cobaltates (Arnacnac)MgCo(COD)2 (1-3) were synthesised by reacting (Arnacnac)MgI(OEt2) with K[Co(η4-COD)2] (COD = 1,5-cyclooctadiene) [Arnacnac = CH(ArNCMe)2; Ar = 2,4,6-Me3-C6H2 (Mes), 2,6-Et2-C6H3 (Dep), 2,6-iPr2-C6H3Mes (Dipp)]. Compounds 1-3 form contact ion-pairs in toluene, while solvent separated ion-pairs are formed in THF. The effect of ion-pairing on the reactivity is illustrated by reaction of 2 with tert-butylphosphaalkyne, which affords distinct 1,3-diphosphacyclobutadiene complexes. The heteroleptic sandwich complex [(Depnacnac)MgCo(P2C2tBu2)]2 (4) is selectively formed in toluene, while the homoleptic bis(1,3-diphosphacyclobutadiene) complex [(Depnacnac)Mg(THF)3][Co(P2C2tBu2)2] (5) is obtained in THF. Complex 4 is a precursor to further unusual phosphaorganometallic compounds. Substitution of the labile COD ligand in 4 by white phosphorus (P4) enabled the synthesis of the phosphorus-rich sandwich compound [(Depnacnac)MgCoP4(P2C2tBu2)]2 (6). The heterobimetallic complex (Cp*NiP2C2tBu2)Co(COD) (7) was isolated after treatment of 4 with Cp*Ni(acac) (Cp* = C5Me5, acac = acetylacetonate).

Reactivity of P4 butterfly complexes towards NHCs - generation of a metal-bridged P2 dumbbell complex

The reactivity of the P₄ butterfly complexes [{Cp'''Fe(CO)₂}₂(μ,η^1:1-P₄)] (A, Cp''' = C₅H₂^tBu₃) and [{Cp*Cr(CO)₃}₂(μ,η^1:1-P₄)] (B, Cp* = C₅(CH₃)₅) towards the N-heterocyclic carbene IMe (1,3,4,5-tetramethyl-imidazol-2-ylidene) is reported. The reaction of A affords [P(IMe)₂][Fe(CO)₂Cp'''] (1) or [P(IMe)₂][{Cp'''Fe}₂(μ,η^3:3-P₃)] (2), the latter possessing a P₃-allylic moiety. In contrast, the reaction of B yields [P(IMe)₂][Cr(CO)₃Cp*] (3) and [{Cp*Cr(CO)₂}(η²-P₂IMe₂)][Cr(CO)₃Cp*] (4), featuring a novel metal-bridged P₂ dumbbell.

Coordination Behavior of a P4 -Butterfly Complex towards Transition Metal Lewis Acids: Preservation versus Rearrangement

The reactivity of the P4 butterfly complex [{Cp'''Fe(CO)2 }2 (μ,η1:1 -P4 )] (1, Cp'''=η5 -C5 H2 tBu3 ) towards divalent Co, Ni and Zn salts is investigated. The reaction with the bromide salts leads to [{Cp'''Fe(CO)2 }2 (μ3 ,η2:1:1 -P4 ){MBr2 }] (M=Co (2Co), Ni (2Ni), Zn (2Zn)) in which the P4 butterfly scaffold is preserved. The use of the weakly ligated Co complex [Co(NCCH3 )6 ][SbF6 ]2 , results in the formation of [{(Cp'''Fe(CO)2 )2 (μ3 ,η4:1:1 -P4 )}2 Co][SbF6 ]3 (3), which represents the second example of a homoleptic-like octaphospha-metalla-sandwich complex. The formation of the threefold positively charged complex 3 occurs via redox processes, which among others also enables the formation of [{Cp'''Fe(CO)2 }4 (μ5 ,η4:1:1:1:1 -P8 ){Co(CO)2 }][SbF6 ] (4), bearing a rare octaphosphabicyclo[3.3.0]octane unit as a ligand. On the other hand, the reaction with [Zn(NCCH3 )4 ][PF6 ]2 yields the spiro complex [{(Cp'''Fe(CO)2 )2 (μ3 ,η2:1:1 -P4 )}2 Zn][PF6 ]2 (5) under preservation of the initial structural motif.

From a P4 butterfly scaffold to cyclo- and catena-P4 units

The reactivity of [{Cp'''Fe(CO)2}2(μ,η1 : 1-P4)] (1) towards half-sandwich complexes of Ru(ii), Rh(iii), and Ir(iii) is studied. The coordination of these Lewis acids leads to a rearrangement of the P4 butterfly unit to form complexes with either an aromatic cyclo-P4R2 unit (R = Cp'''Fe(CO)2) or a catena-tetraphosphaene entity.