Organometallics 1989, 8, 2065-2068
to no reaction a t all after 20 h, in striking contrast to 2 which incorporates 99 % of benzaldehyde under analogous conditions (vide infra). Therefore, we suggest that the reaction goes through the seven-membered intermediate A rather than the four-membered one B. In the absence of a ketone, the aldehyde adduct 3 is solely converted into the acetal 4. When a ketone is present, the exchange reaction leading to the ketone adducts 5 competes with the aldehyde acetal formation. This exchange reaction, which may proceed via the intermediate C, proceeds more rapidly than the direct addition of ketone to 2 (vide infra). The exchange process is supported by the following observations. (1)In contrast to the acceleration of ketone reactions, the reaction rates of the aldehyde partners are diminished. (2) The exchange occurs between aldehydes as well. When a 1:l mixture of hexanal and nonanal is used, the reaction of the latter is accelerated, while the rate of the former with a smaller 7,-, value remains at the about level of the control reaction (entry 12). More dramatic are the reactions with p-nitro- and pentafluorobenzaldehyde that are virtually inert toward the distannoxane-catalyzed acetalization (see Table I). The reactions of these compounds are greatly accelerated on addition of octanal (1 equiv) whose 7 value is increased (entries 13, 14). Thus, the acetals of these less reactive aldehydes are accessible in 72% yield after 8 h for p-nitrobenzaldehyde and 84% yield after 5 h for pentafluorobenzaldehyde. No such acceleration takes place between ketones, a quite reasonable result in terms of the slow initial uptake of ketone by 2 (entry 15). In the hope of obtaining further confirmation of this novel transcarbonylation, the stoichiometric reaction of 2 with carbonyl compounds has been monitored by means of GLC analysis. The failure to isolate 2 in pure form led us to make use of an in situ formed compound. A benzene solution of 1 and ethylene glycol (1:l molar ratio) is heated azeotropically for 3 h.6 Benzaldehyde (1equiv) is added to this solution, and then the mixture is heated under reflux. After 20 h, the GLC peak of benzaldehyde had almost disappeared, showing that at least 99% of the aldehyde has been consumed. Occurrence of 3 can be deduced from the fact that no acetal is detected. Addition of 2-octanone (1 equiv) to this reaction mixture at this stage induces the exchange reaction. After 20 h, 39% of the 2-octanone had disappeared while the benzaldehyde peak reappeared indicative of a 25% recovery on the basis of the initially employed amount. Note that the reaction of 2-octanone with 2 under similar conditions occurs more sluggishly (10% after 20 h). Apparently, the reaction of ketone with 3 proceeds more easily than that with 2. In conclusion, a distannoxane has proved to activate less reactive carbonyl compounds in an unprecedented manner. In contrast to the biased equilibrium between 2 and 5 to the side of the former, the equilibrium between 3 and 5 is more balanced. The susceptibility of 5 to be converted into 6 also assists the shift from 3 to 5 . Finally, also noteworthy from the synthetic point of view is that various functional groups remain intact in this acetalization since the reaction proceeds under almost neutral The synthetic utility is the subjects of future work. Acknowledgment. This work was partially supported by Grant-in-Aid from The Ministry of Education, Science, and Culture, Japan, and by CIBA-GEIGY Foundation for the Promotion of Science, Takarazuka, Japan. (6) Evaporation of the benzene solvent leaves amorphous powders. Although the 'H NMR spectrum suggests the formation of the desired compounds, purification has not yet been successful.
2065
Registry No. 1, 95971-04-3;4 (R' = ~C5H11,R2 = H), 351594-4;4 (R' = n-C7H15,R2 = H), 4359-57-3;4 (R' = n-C8H17,R2 = H), 5432-30-4; 4 (R' = t-C4H9,R2 = H), 2568-29-8;4 (R' = C6H5, R2 = H), 936-51-6;4 (R' = n-C6Hl3, R2 = CH,), 937-94-0;6 (R3 = p-NO2CsH4,R4 = H), 2403-53-4;6 (R3 = CsF5, R4 = H), 19161-34-3; 6 (R3 = n-CjHll, R4 = CH3), 4352-95-8;6 (R3, R4 = C2Hj), 4362-57-6;6 (R3 = CsH5, R4 = CH,), 3674-77-9;nC5H11CH0, 66-25-1;n-CsH&HO, 111-71-7; n-C7H&HO, 12413-0;n-CsH17CHO,124-19-6; i-CdHgCHO, 590-86-3;t-C,H,CHO, 630-19-3; CBHjCHO, 100-52-7; p-NO&GH,CHO, 555-1644;C$5n-CjHiICOCH3, 110-43-0; n-CsH13COCH3, 111CHO, 653-37-2; 13-7;C2HjCOC2Hj,96-22-0;PhCOCH3, 98-86-2;2-hexanyl-1,32-(2-methylpropyl)-1,3-dioxolane, 6135-52-0; dioxolane,1708-34-5; 1-(2-methoxyethoxy)-3-isothiocyanatotetraorganodistannoxane, 121471-39-4.
Characterization of an Intermediate in the Reaction of a Cationic Carbonyl Complex with Secondary Amine To Glve a Carbamoyl Complex Li Huang, Fumiyuki Orawa," Kohtaro Osakada, and Akio Yamamoto" Research Laboratory of Resources Utilization Tokyo Institute of Technology, 4259 Nagatsuta Midori-ku, Yokohama 227, Japan Received March 13. 1989
Summary: Reaction of trans - [Pd(COPh)(CO)(PMe,),] BF, (1) with pyrrolidine affords a cationic benzoylpalladium complex with an 0-protonated carbamoyl group, trans -
-
[ Pd(COPh){C(OH)(N(CH,),CH,))(
PMe,),] BF, (2b), which has been characterized by means of NMR spectroscopy. Complex 2b reacts further with pyrrolidine to give benzo y I- c a r ba m oy I c o m p I e x trans Pd(C 0Ph ) (C0-
-
-
(3) together with the pyrrolidinium salt
N(CH,),CH,)(PMe,),
CH,(CH,),NH,BF,. The conversion of 2b to 3 is a reversible process, and treatment of 3 with the pyrrolidinium salt regenerates 2b. The 0-protonated carbamoyl structure of 2b is supported by X-ray structural analysis of its 0-alkylated analogue trans - [Pd(COPh){C(OEt)-
-
-
N(CH,),CH,))(PMe,),]
BF, (4), which has been prepared by
reaction of trans -Pd(COPh)(CON(CH,),CH,)(PMe,), Et,OBF,.
with
Transition-metal carbonyl complexes are known to react with amines, alcohols, and water to give carbamoyl, alkoxycarbonyl, and hydroxycarbonyl complexes, respectively.' These complexes are postulated as key intermediates in various transition-metal-catalyzed carbonylation reactions. The following is a generally accepted reaction course.2 CLnM-COl+
*NUH
A
