Syntheses and reactions of a cationic hydrido(hydroxymethyl)iridium complex. The crystal and molecular structure of hydrido(hydroxymethyl)tetrakis(trimethylphosphine)iridium(III) hexafluorophosphate, [IrH(CH2OH) (PMe3)4][PF6]
Abstract:Syntheses and Reactions of a Cationic Hydrido(hydroxymethyl)iridium Complex. The Crystal and Molecular Structure of Hydrido(hydroxy methyl)tetrakis(trimethy Iphosphine) iridium (III) Hexafluorophosphate, [IrH(CH2OH)(PMe3)4][PF6p
“…Compound 6 has been fully characterized by NMR, including 2D experiments. The obtained spectra confirm the formation of the hydroxyalkyl groups bonded to rhodium, , trans to the phosphorus atom of the acyl−phosphine chelate. The 13 C resonances appear in the 93−97 ppm range as doublets of doublets due to coupling with rhodium ( J (Rh,C) = 22 Hz) and with a trans phosphorus atom ( J (P,C) = 98 Hz).…”
Section: Resultsmentioning
confidence: 99%
“…Complex 6 shows lower stability than the related compound [Rh(PPh 2 ( o -C 6 H 4 CO))(PPh 2 ( o -C 6 H 4 CHOH))(bdh)]BPh 4 ,15a containing a better donor ligand such as the bidentate diimine instead of pyridine and chloride. This is not surprising,12a but the usual decomposition paths reported for hydroxyalkyl complexes include regeneration of the M−H bond and free aldehyde or, if an acid is added, disproportionation with hydride transfer to yield an acyl and an alkyl complex. , No presence of 5 was observed in the NMR spectra recorded during the transformation of 6 into 8 , thus excluding the reversal of 6 into 5 . 3 …”
[RhCl(COD)]2 (COD = 1,5-cyclooctadiene) reacts with o-(diphenylphosphino)benzaldehyde (PPh2(o-C6H4CHO)) (Rh/P = 1:1) in the presence of pyridine to give an acyl hydrido species, [RhHCl(PPh2(o-C6H4CO))(py)2] (1). In chlorinated solvents exchange of hydride by chloride gives [RhCl2(PPh2(o-C6H4CO))(py)2] (2). The reactions of 1 with PPh3 and of 2 with biacetyl dihydrazone (bdh) gives the
pyridine substitution products [RhHCl(PPh2(o-C6H4CO))(PPh3)(py)] (4) and [RhCl2(PPh2(o-C6H4CO))(bdh)] (3), respectively. By using a 1:2 ratio of Rh to PPh2(o-C6H4CHO) [RhHCl(PPh2(o-C6H4CO))(κ1-PPh2(o-C6H4CHO))(py)] (5) with trans phosphorus atoms is formed. The aldehyde group may undergo
two different reactions. In benzene 5 affords the acyl hydroxyalkyl species [RhCl(PPh2(o-C6H4CO))(PPh2(o-C6H4CHOH))(py)] (6) with cis phosphorus atoms, via a pyridine dissociation path. 6 undergoes
dehydrogenation, with H2 evolution, to afford the diacyl derivative [RhCl(PPh2(o-C6H4CO))2(py)] (8),
which shows fluxional behavior in solution, with the values ΔH
⧧ = 8.8 ± 0.4 kcal mol-1 and ΔS
⧧ =
−16.7 ± 1 eu. Opening of the acylphosphine chelate appears to be responsible for the fluxionality. In
methanol 5 undergoes displacement of chloride by the aldehyde to afford the cationic acyl hydrido aldehyde
[RhH(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4CHO))(py)]+ (10), which can be isolated if precipitated immediately with an appropriate counterion. Longer reaction periods of 5 in methanol solution lead to a
mixture of the diacyl 8 and the cationic acyl hydrido alcohol [RhH(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4CH2OH))(py)]+ (11). The spectroscopic characterization of some intermediates in this reaction evidence
a bimolecular ionic mechanism as being responsible for the hydrogenation of the aldehyde with the
hydroxyalkyl 6 being the source of both proton and hydride. Complex 11 can also be obtained by the
reaction of 5 with NaBH4 in methanol solution.
“…Compound 6 has been fully characterized by NMR, including 2D experiments. The obtained spectra confirm the formation of the hydroxyalkyl groups bonded to rhodium, , trans to the phosphorus atom of the acyl−phosphine chelate. The 13 C resonances appear in the 93−97 ppm range as doublets of doublets due to coupling with rhodium ( J (Rh,C) = 22 Hz) and with a trans phosphorus atom ( J (P,C) = 98 Hz).…”
Section: Resultsmentioning
confidence: 99%
“…Complex 6 shows lower stability than the related compound [Rh(PPh 2 ( o -C 6 H 4 CO))(PPh 2 ( o -C 6 H 4 CHOH))(bdh)]BPh 4 ,15a containing a better donor ligand such as the bidentate diimine instead of pyridine and chloride. This is not surprising,12a but the usual decomposition paths reported for hydroxyalkyl complexes include regeneration of the M−H bond and free aldehyde or, if an acid is added, disproportionation with hydride transfer to yield an acyl and an alkyl complex. , No presence of 5 was observed in the NMR spectra recorded during the transformation of 6 into 8 , thus excluding the reversal of 6 into 5 . 3 …”
[RhCl(COD)]2 (COD = 1,5-cyclooctadiene) reacts with o-(diphenylphosphino)benzaldehyde (PPh2(o-C6H4CHO)) (Rh/P = 1:1) in the presence of pyridine to give an acyl hydrido species, [RhHCl(PPh2(o-C6H4CO))(py)2] (1). In chlorinated solvents exchange of hydride by chloride gives [RhCl2(PPh2(o-C6H4CO))(py)2] (2). The reactions of 1 with PPh3 and of 2 with biacetyl dihydrazone (bdh) gives the
pyridine substitution products [RhHCl(PPh2(o-C6H4CO))(PPh3)(py)] (4) and [RhCl2(PPh2(o-C6H4CO))(bdh)] (3), respectively. By using a 1:2 ratio of Rh to PPh2(o-C6H4CHO) [RhHCl(PPh2(o-C6H4CO))(κ1-PPh2(o-C6H4CHO))(py)] (5) with trans phosphorus atoms is formed. The aldehyde group may undergo
two different reactions. In benzene 5 affords the acyl hydroxyalkyl species [RhCl(PPh2(o-C6H4CO))(PPh2(o-C6H4CHOH))(py)] (6) with cis phosphorus atoms, via a pyridine dissociation path. 6 undergoes
dehydrogenation, with H2 evolution, to afford the diacyl derivative [RhCl(PPh2(o-C6H4CO))2(py)] (8),
which shows fluxional behavior in solution, with the values ΔH
⧧ = 8.8 ± 0.4 kcal mol-1 and ΔS
⧧ =
−16.7 ± 1 eu. Opening of the acylphosphine chelate appears to be responsible for the fluxionality. In
methanol 5 undergoes displacement of chloride by the aldehyde to afford the cationic acyl hydrido aldehyde
[RhH(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4CHO))(py)]+ (10), which can be isolated if precipitated immediately with an appropriate counterion. Longer reaction periods of 5 in methanol solution lead to a
mixture of the diacyl 8 and the cationic acyl hydrido alcohol [RhH(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4CH2OH))(py)]+ (11). The spectroscopic characterization of some intermediates in this reaction evidence
a bimolecular ionic mechanism as being responsible for the hydrogenation of the aldehyde with the
hydroxyalkyl 6 being the source of both proton and hydride. Complex 11 can also be obtained by the
reaction of 5 with NaBH4 in methanol solution.
“…Many hydroxymethyl complexes have now been synthesized and studied. 29,30,31,[33][34][35][36][37][38][39][42][43][44][45][46][47][48][49][50][51][52][53] Berke and Huttner51 first showed that CO migratory insertion into the metalhydroxymethyl bond occurs in the unstable complex Fe-(CO)2[P(OMe)3]2(Cl)(CH2OH). An isolated metallacyclic rhenium hydroxyalkyl complex was later shown by Gla-dysz53 to react with CO (eq 4).…”
“…Indeed, PMe3 dissociation from this complex is very difficult. 4 In addition, the Ir"' complexes that would be formed by attack at the metal, (PMe3)41r(R)(SiMe3)+ are expected to be stable towards Si-R reductive elimination at 25°C. For example, heating at 100°C is required in order to cause reductive elimination from mer-(PMe3)31r(H)(SiR3)(Me) (R = Et, Ph, Et0).6 Also, (PMe3)41rMe(H)+ is thermally stable.2…”
Me3SiOTf (Tf = CF3SO2) is a useful reagent for electrophilic abstraction reactions involving electron-rich complexes RlrL, (R = H, CI, Me, Ph; L = PMe3, PEt,); direct external attack of Me3Si+ on R is probably involved.Generation of vacant coordination sites by ligand abstraction is commonplace in inorganic and organometallic chemistry. Normally, this abstraction is based on generation of insoluble salts, such as when Ag+ or T1+ are used for halide abstraction. However, with electron-rich, low-valent complexes, this may be a problematic procedure because of competing electron transfer processes. Thus, in our attempt to abstract the chloride ligand from I I -( P E ~~) ~C I 1 with Ag+, immediate formation of silver metal and uncharacterized iridium complexes took place. By contrast, reaction of 1 with trimethylsilyl triflate, Me3SiOTf 21 at room temperature in benzene results in immediate quantitative formation of the novel iridiacycle 3t and Me3SiC1$ [eqn( l)]. M3P ti PEt2 Ir(PEt3)3CI + Me3SiOTf -'/(d + Me3SiCI (1) 1 2 Et3P'LT, 3
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