To “Dress” the “Naked” Acetylide with Metal Complexes: How and Why?

Abstract

The high mobility of the C22− ligand in trinuclear complexes of the type [M]3C2 (shown schematically) and alkynyl‐bridged [M]2C2R complexes provides information for attaining a better understanding of the topomerization processes of alkyne complexes and alkynes via vinylidene complexes [M]CCR2 and vinylidenes :CCR2, respectively, in which the carbon atoms exchange their positions.

Recent Synthetic and Catalytic Applications of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes

“…[2] Additionally, there are well defined complexes, in which the coordinatively and electronically unsaturated complex fragments [Cp′ 2 M] are stabilized in Cp′ 2 M(L) n by well suited ligands L as for example in the complexes Cp 2 Ti(PMe 3 ) 2 introduced by Rausch and Alt et al [3] Cp 2 Ti[(P(OEt) 3 ] 2 [4] and the here described complexes Cp′ 2 M(L)(η 2 -btmsa), btmsa = bis(trimethylsilyl)acetylene, with or without L such as pyridine or THF. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] There exist several methods to prepare such bis(trimethylsilyl)acetylene complexes Cp′ 2 M(η 2 -Me 3 SiC 2 SiMe 3 ) as starting materials. As typical examples for the complexes with unsubstituted Cp ligands the compound Cp 2 Ti(η 2 -Me 3 SiC 2 SiMe 3 ) was firstly obtained in 1988 by the reduction of Cp 2 TiCl 2 with magnesium in the presence of Me 3 SiC≡CSiMe 3 in THF at room temperature, [24b] later in 1993 by the reduction of Cp 2 TiCl 2 with n-butyllithium in n-hexane and adding Me 3 SiC≡CSiMe 3 at -78°[ 24c] as well as in 2010 by the reaction of Cp 2 TiMe 2 with Me 3 SiC≡CSiMe 2 H at 60°C in n-hexane.…”

“Guilty” Verdict—Evidence for the Noninnocence of Cyanide

“…In contrast to the cyanide case, a reduced CO has thus been discussed [15c,d] for several "super-reduced" carbonylmetalates. [15a,b] On the other hand, the C 2 2À ion, À CC À , (bridging acetylide), [22] another diatomic 10-electron species, may also behave in a noninnocent way as illustrated by the binding modes in Figure 2. However, the oxidation state formalism is rarely employed in this area of organometallic chemistry.…”

Advantages of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes as Metallocene Sources Towards Other Synthetically used Systems

“…The first example of a group 4 metallocene alkyne complex without additional ligands Cp 2 Ti(η 2 ‐btmsa) with bis(trimethylsilyl)acetylene and a series of similar complexes Cp′ 2 M(η 2 ‐btmsa) (M=Ti, Zr, Hf; Cp′=Cp, Cp*=η 5 ‐pentamethylcyclopentadienyl and Cp′ 2 = rac ‐(ebthi) as rac ‐1,2‐ethylene‐1,1′‐bis(η 5 ‐tetrahydroindenyl) and others were intensively investigated (Scheme ) …”

“…Based on this simple substitution reaction, Cp 2 Ti(η 2 ‐btmsa) and similar complexes were applied as excellent sources for the generation of the very reactive coordinatively and electronically unsaturated complex fragments [Cp′ 2 M]. These were used in many synthetic and catalytic reactions, summarized before in several papers and some reviews . Nevertheless, some very view examples exist in which the substitution of the bis(trimethylsilyl)acetylene ligand did not work and a coupling of the alkyne with other substrates was found …”

“…Systems that are more prone to ligand substitution include those possessing neutral placeholder ligands such as Cp 2 Ti(PMe 3 ) 2 , Cp 2 Ti(P[OEt) 3 ] 2 , [Cp* 2 Ti(N 2 )] 2 N 2 and others like Cp 2 Ti(CO) 2 as well as alkyne complexes of the type Cp′ 2 M(L)(η 2 ‐btmsa) (btmsa=bis(trimethylsilyl)acetylene; with or without L, L=pyridine or THF) …”