Effect of the Substitution on the Protonation of Allyl Cyclopentadienyl Molybdenum(II) Compounds

Abstract

Synthesis, characterization, and reactivity of new allyl cyclopentadienyl molybdenum(II) compounds [(η 3 -C 3 H 4 R 1 )(η 5 -C 5 H 3 (R 2 ) 2 )Mo(CO) 2 ] (R 1 = H, COOMe; R 2 = COOMe, CONH t Bu) are reported. Although these compounds are structural analogues of [(η 3 -C 3 H 5 )(η 5 -Cp)Mo-(CO) 2 ], their reactivity is very different. While protonation of [(η 3 -C 3 H 5 )(η 5 -Cp)Mo(CO) 2 ] gives a cationic cyclopentadienyl complex, the presented compounds give cationic allyl complexes [(η 3 -C 3 H 4 R)Mo(CO) 2 (NCMe) 3 ][BF 4 ] (R = H, COOMe) or stable cationic allyl cyclopentadienyl complexes. The theoretical calculations have shown that this behavior is a result of high affinity of the functional groups in the cyclopentadienyl ligand toward protonation.

Acyl‐Functionalized Molybdenum Compounds [(η3‐C3H5)(η5‐Cp′)Mo(CO)2]: An Experimental Study Including the X‐ray Structure of a Rare endo Conformer

“…The reaction of the acetyl derivative 10 reveals a higher resistance towards loss of the allyl ligand than previously reported for the disubstituted ester-and amide-functionalized derivatives [(η 3 -C 3 H 5 ){η 5 -C 5 H 3 (COR) 2 }Mo(CO) 2 ] (R = OMe; NHtBu) [5] (26) was observed. Of course, a 1,2-substituted arrangement should considerably simplify the protonation of the carboxylic acid derivatives.…”

“…[6] In the presence of acetonitrile, it gives a cationic cyclopentadienyl complex [(η 5 4 ], as was evidenced by 1 H NMR spectroscopy. [6] In the presence of acetonitrile, it gives a cationic cyclopentadienyl complex [(η 5 4 ], as was evidenced by 1 H NMR spectroscopy.…”

“…The 1 H NMR data imply that the borderline of the reactivity is not very sharp as treatment of 12 with HBF 4 ·Et 2 O followed by the addition of bpy gives the desired cyclopentadienyl complex [(η 5 The parent benzoyl compound 13 as well as benzoyl derivatives substituted by electron-donating groups (e.g., 14) seem to be more appropriate for synthetic efforts under acidic conditions as both derivatives gave the desired cationic cyclopentadienyl compounds 22 and 23, respectively, without contamination by allyl-molybdenum species (see Scheme 4). To achieve this, the phenylacetyl derivative (12) was used because the electronic properties of -COCH 2 Ph lie between those of the -COMe and -COCF 3 functions.…”

“…[4] In a recent study we found that a similar substitu-tron-withdrawing acyl groups (e.g., -CHO, -COCF 3 ) show different outcomes in the protonation reactions compared with the parent cyclopentadienyl compound or derivatives bearing less electron-withdrawing groups (e.g., -COMe, -COPh). [5,6] A detailed investigation of this phenomenon is of particular importance because the cationic compounds [(η 5 -CpЈ)Mo(CO) 2 (NCMe) 2 ] + are the key precursors to a variety of mono-and bis-cyclopentadienyl molybdenum(II) compounds [7][8][9] that find several applications in biology [10][11][12] and catalysis. An IR spectroscopic analysis revealed that the aldimine-functionalized products formed very quickly even under the mild conditions that fulfill the basic rules of click chemistry.…”

Stabilization of η3-indenyl compounds by sterically demanding N,N-chelating ligands in the molybdenum coordination sphere

“…[15][16][17][18][19][20][21] Recently, we have described a synthesis of [{(h 5 -Ind)Mo(CO) 2 (m-Cl)} 2 ] (1; Scheme 1) that was found to be a versatile synthon for various h 3 -indenyl compounds. 34,35 The aim of this study is to bring a detail description of the coordination properties of [{(h 5 -4,7-Me 2 C 9 H 5 )Mo(CO) 2 (m-Cl)} 2 ] (2) in attempt to synthesize new h 3 -indenyl compounds structurally related with the well-known complexes bearing h 3 -allyl [(h 3 -C 3 H 5 )Mo(CO) 2 ( N,N L)Cl]. 24 Although the cyclopentadienyl and indenyl molybdenum compounds have oen a similar molecular structure, a different reactivity is expected since a replacement of the cyclopentadienyl ligand with the indenyl accelerates reaction rates due to a lower energetic barrier of the haptotropic shi of the p-ligand.…”