Directed Formation of Allene Complexes upon Reaction of Non-heteroatom-Substituted Manganese Alkynyl Carbene Complexes with Nucleophiles

Abstract

The non-heteroatom-substituted alkynyl carbene Cp′(CO) 2 MndC(Tol)CtCPh (1, Cp′ ≡ (η 5 -MeC 5 H 4 )) is first shown to react at low temperature with lithium diorganophosphide LiPR 2 (R ) Ph, Cy) to form an anionic species. Subsequent treatment with CF 3 SO 3 H affords the η 4 -vinylketene complex Cp′(CO) 2 Mn[η 4 -{R 2 P(Ph)CdCHC(Tol)dCdO}] (2; 2a: R ) Ph (70% yield), 2b: R ) Cy (55% yield)) as the major compound, along with trace amounts of the η 2 -allene complex syn-Cp′(CO) 2 Mn[η 2 -{Ph 2 P(Tol)-CdCdC(Ph)H}] (syn-3a) for R ) Ph, or along with the η 2 -allene complex Cp′(CO) 2 Mn[η 2 -{H(Tol)-CdCdC(Ph)PCy 2 }] (4b, 26% yield, 1:2 mixture of syn/anti isomers) for R ) Cy. On the other hand, subsequent treatment with NH 4 Cl aq affords only η 2 -allene complexes, obtained either as a ca. 1:9 mixture of syn-3a and Cp′(CO) 2 Mn[η 2 -{H(Tol)CdCdC(Ph)PPh 2 }] (4a) (75% yield) for R ) Ph or as a 1:2 mixture of syn-and anti-4b for R ) Cy (74% yield). Combined NMR and single-crystal X-ray diffraction studies (for 2a, anti-4b, and syn-4b) revealed that both type 2 and type 4 species result from a nucleophilic attack of the diorganophosphide onto the remote alkynyl carbon atom in 1 (C γ ), whereas type 3 species results from a nucleophilic attack of the carbene carbon atom (C R ). Complexes 3a and 4a,b are prone to undergo a thermal rearrangement to give the η 1 -phosphinoallene complexes Cp′(CO) 2 Mn[η 1 -{Ph 2 P(Tol)CdCdC(Ph)H}] (5a) and Cp′(CO) 2 Mn[η 1 -{R 2 P(Ph)CdCdC(Tol)H}] (6; 6a: R ) Ph, 6b: R ) Cy), respectively. Reaction of 1 with p-toluenethiol in the presence of NEt 3 (20%) affords a 1.8:1 mixture of Cp′(CO) 2 Mn[η 2 -{TolS(Tol)CdCdC(Ph)H}] (syn-11), resulting from a nucleophilic attack at C R in 1, and Cp′(CO) 2 Mn[η 2 -{H(Tol)CdCdC(Ph)STol}] (12), resulting from a nucleophilic attack at C γ , whereas treatment of 1 with lithium p-toluenethiolate at -80 °C followed by protonation with NH 4 Cl aq gave the same syn-11 and 12 complexes now in a 1:2.3 ratio. Finally, 1 was found to react with cyclohexanone lithium enolate to afford, upon protonation, the η 2 -allene complex Cp′(CO) 2 Mn[η 2 -{H(Tol)CdCdC(Ph)CH(CH 2 ) 4 C(O)}] (syn-13), resulting from a nucleophilic attack at C γ in 1. The solidstate structures of syn-11 and syn-13 are also reported.

Synthesis of η1-α-Phosphinocarbene Complexes of Manganese and Mechanistic Insight into Their Base-Induced Transformations

“…Complex [ 7a ]Li exhibits a three-band pattern in the ν CO region (IR (THF): 1882 (vs), 1811 (s), 1772 (s) cm −1 (ν CO )), very similar to the one observed for the carbene anion [Cp′(CO) 2 MnC(OEt)CH 2 ]Li (IR (THF): 1870 (vs), 1795 (s), 1745 (s) cm −1 (ν CO )) or for the η 1 -allenyl anion [Cp′(CO) 2 Mn−C(Ph)CC(Tol)Nu]Li (Nu = H, STol, PPh 2 ) (IR (THF): 1873 (vs), 1798 (s), 1755 (s) cm −1 (ν CO )) . The occurrence of a three-band pattern in these anionic dicarbonyl species was previously ascribed to an interaction of lithium cations with the oxygen atom of a CO group, and it seems likely that the same phenomenon takes place here.…”

“…For our part, inspired by Fischer’s seminal work and engaged for some time in a general program aimed at exploiting the availability, ease of use, and high reactivity of cationic manganese carbyne complexes derived from cymantrene, we envisioned that the deprotonation α- phosphonio carbene complexes resulting from nucleophilic attack of secondary and/or primary phosphine on such carbyne species would possibly afford η 1 -α-phosphinocarbene complexes. In a preliminary communication of the present work, such an approach was found to be viable, offering multiple advantages, such as (i) the simplicity of the procedure, (ii) the absence of constraints about the steric bulk of phosphorus substituents, and (ii) the simplicity and diversity of the phosphorus sources, often being commercially available.…”

A Direct, Modular, and Efficient Construction of the PCP Structural Motif through Coupling of Manganese Carbyne Complexes with Phosphines

“…Having in mind the aim to exploit this original carbyne/phosphine/phosphine coupling for the synthesis of valuable chemicals, we next focused on means to efficiently liberate the resulting diphosphines from the robust manganese complexes ( 4 → 5 , Scheme ). Inspired by the high yield photochemical liberation of cyclopentadienes8 or allene6b from cymantrene derivatives, we first investigated the behavior of the model complex Mp(PPh 3 ) ( 6 ) under visible light irradiation in different solvents (Table 1).…”

Nitrogen, phosphorus, arsenic, antimony and bismuth

“…86 In a related study the treatment of the manganese alkynyl carbene species Mn(Z 5 -C 5 H 4 Me)(CO) 2 (QC{p-tol}CRCR) with lithium reagents LiPR 2 (R = Ph, Cy) followed by protonation of the resulting anions has been reported. 87 Products arising from attack on the carbene carbon and the terminal alkynyl carbon were observed. The synthesis and reactivity of the oxophosphinidine complex Mo(Z 5 -C 5 H 5 ){P(O)R}(CO) 2 (SnPhCl 2 ) has also been described.…”