Homoleptic and heteroleptic Au(i) complexes containing the new [Co5C(CO)12]− cluster as ligand

Abstract

The new [{Co5C(CO)12}Au{Co(CO)4}](-), , cluster has been obtained from the reaction of [Co6C(CO)15](2-) with two equivalents of [AuCl4](-). reacts with an excess of HBF4 resulting in the formation of [{Co5C(CO)12}2Au](-), . The new derivatives [Co5C(CO)12(AuPPh3)], , and [Co5C(CO)11(AuPPh3)3], , have been obtained by reacting with two and four equivalents of [Au(PPh3)Cl], respectively. All the new species have been structurally characterised by means of X-ray crystallography as their [NEt4][], [NEt4][], [NMe3(CH2Ph)][], and thf·0.5C6H14 salts and solvates. may be viewed as a homoleptic Au(i) complex containing two [Co5C(CO)12](-) clusters as ligands. Similarly, and are heteroleptic Au(i) complexes containing one [Co5C(CO)12](-) cluster ligand as well as [Co(CO)4](-) or PPh3. Conversely, contains the [Co5C(CO)11](3-) cluster stabilized by three [AuPPh3](+) fragments. and have been investigated in solution by means of electrochemical and spectroelectrochemical methods, revealing a very rich redox propensity to form the closely related (n = 1-3) and (n = 0-3) species.

Co5C and Co4C carbido carbonyl clusters stabilized by [AuPPh3]+ fragments

“…The neutral [Co 5 C(CO) 11 (AuPPh 3 ) 3 ], 1 (isomer 1-A), cluster has been previously isolated in very low yields as 1-AÁthfÁ0.5C 6 H 14 whilst studying the reaction of [{Co 5 C(CO) 12 } 2 Au] À with four equivalents of [Au(PPh 3 )Cl] (Scheme 1) [15]. At the same time, we have reported that [Co 6 C(CO) 15 ] 2À reacts with 2-3 equivalents of [Au(PPh 3 )Cl] resulting in [Co 6 C(CO) 12 (AuPPh 3 ) 4 ] [24].…”

“…These are the only Co 5 C and Co 4 C carbonyl clusters containing semi-exposed carbides, and all of them do not exist as free species but require coordination to cationic fragments in order to be stable. A possible explanation is that in the case of Group VIII metals the M 5 C and M 4 C frames are stabilized by [14][15][16] respectively, which saturate the surface of the clusters and ensure steric protection. Conversely, the hypothetical [Co 5 C(CO) 12 ] À , [Co 5 C(CO) 11 ] 3À and [Co 4 C(CO) 10 ] 2À clusters contain fewer CO ligands which do not guarantee steric protection resulting in an enhanced reactivity.…”

“…One isomer of 1 (1-A) has been previously reported, and a second isomer 1-B will be herein described. Clusters 3 and 5 will be compared to the isostructural 4 reported in a previous paper [15]. 1-6 contain [Co 5 C(CO) 12 ] À , [Co 5 C(CO) 11 ] 3À and [Co 4 C(CO) 10 ] 2À cores stabilized by the interaction to [AuPPh 3 ] + fragments, which further confirm their ability to coordinate to anionic metal carbonyl clusters and stabilize unprecedented species [17][18][19][20][21][22][23].…”

“…We have recently reported the [{Co 5 C(CO) 12 }Au{Co(CO) 4 }] À , [{Co 5 C(CO) 12 } 2 Au] À and [Co 5 C(CO) 12 (AuPPh 3 )], 4, clusters which contain a square pyramidal 74 CVE [Co 5 C(CO) 12 ] À fragment stabilized by coordination to miscellaneous Au(I) centers, as well as [Co 5 C(CO) 11 (AuPPh 3 ) 3 ], 1-A, comprising a 74 CVE [Co 5 C(CO) 11 ] 3À core stabilized by three [AuPPh 3 ] + fragments [15]. In addition, [Co 4 C(CO) 10 [16].…”

“…Conversely, semiinterstitial carbide clusters are less common and this is likely to be a consequence of the greater reactivity of exposed or semiexposed carbides. Almost all of the known carbonyl clusters containing semi-interstitial carbides belong to two categories: (a) square pyramidal M 5 C clusters possessing 74 Cluster Valence Electrons (CVE) such as [M 5 C(CO) 15 16 ] 2À [10]; (b) butterfly M 4 C clusters possessing 62 CVE such as [HFe 4 C(CO) 12 ] À [11], [Fe 4 C(CO) 12 ] 2À [12], [Fe 3 RhC(CO) 12 ] À [13], [Os 3 MnC(CO) 13 ] À [14]. Most of these clusters are based on Group VIII Metals, whereas as free species they are unknown for Group IX Metals.…”