'796 Inorganic Chemistry, Vol. 14, No. 4, 1975
Charles
P.Casey and Charles A. Bunnell
Contribution from the Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706
CHARLES P. CASEY* and CHARLES A. BUNNELL
Received April 17, 1974
AIC402494
o-Carbomethoxybenzoylpentacarbonylmanganese(I)9la, was prepared by reaction of NaMn(C0)s with the corresponding acid chloride. l a undergoes bisdecarbonylation in CHC13 at 50' to give o-carbomethoxyphenyltetracarbonyimanganese(I), 221, in which the carbomethoxy group acts as a chelating ligand. N o monodecarbonylated material was observable by spectral means. Decarbonylation of l a in the presence of 4-ethyl-2,6,7-trioxa-l-phosphabicyclo[2.2.2]oc~ane, ETPO, gives only the ETPO substitution product o-carbomethoxybenzoyl(ET~O)tetra~arbonylmanganese(I), Ib. The rate of disappearance of l a in the presence of ETPO is independent of ETPO concentration. Table I. Infrared Spectra
~~~~~~~~~~~~
In the course of studying the reactions of liihium reagents with acylpentacarbonylmanganese compounds, we required a sample of o-carbomethoxybenzoylpentacarbonylmanganese(l), la. This compound was found to lose two molecules of carbon monoxide slowly a t 25" to give ocarbomethoxyphenyltetracarbonylmanganese(I), 2a, in which the carbomethoxy group acts as a chelating ligand. Several compounds containing a chelating carbonyl group have been obtained previously by less straightforward routes.1 A related imine analog of 2a has also been reported.2 Here we present our findings concerning the rate and mechanisms of the conversion of l a to 2a. I
C $0
-- Str freq, cm-'
Compd -
Ibb
2a" 2bb 3b
Heptane.
_
l
_
-
l
I
-
l
2118 m , 2063 m, 2025 s, 2014 s, 1999 s, 1728 w, 1630 w 2086 m, 2018 s, 1994 s, 1718 w, 1600 w, 1591 WJ 2085 m, 1997 s, 1947 s, 1617 w, 1610 in, 1578 w 2024 s, 1953 s, 1908 s, 1612 m 2115 m , 2050 m , 2025 s, 2006 s, 1635 m
121a
a
.
CHCl,.
-
/
Mn(CO),L H4 2a, L = co l a , L = co b, L = ETPO b , E = ETPO ETPO = 4-ethyl 2,6,7-trioxa-l -phosphabicyclo [ 2.2.2loctane
11 was prepared in 60% yield from o-carbomethoxybenzoyl chloride and N a M n ( C 0 ) s in tetrahydrofuran (THF) a t 0'. The infrared spectrum of la (Table I) contained bands at 1728 cm-1 due to the carbomethoxy group and 1630 cm-1 due to the benzoylmanganese moiety. In addition, five bands were obseived in the metai carbonyl region. The nmr spectrum of l a is remarkable in that all four aromatic hydrogens have widely different chemical shifts and give rise to first-order multiplets (Figure 1). The assignment of the HIand W4 resonances in l a was made on the basis of chemical shift comparisons with closely related compounds. The downfield resonance a t 6 7.97 was assigned to Hi, the proton adjacent to the ester group; for comparison, the proton adjacent to the ester group appears at 6 7.70 in dimethyl phthalate, a t 6 7.77 in methyl o-isopropylkenzoate, 3, and at 6 8.05 in methyl benzoate. The upfield resonance of l a at 6 7.19 was assigned to H4, the proton ortho to the acylmanganese group: for comparison, the ortho protons in benzoylpentacarbonylmanganese appear a t 6 7.46 and the proton ortho io the acylrnanganese group in 3 appears at 6 7.2. The chemical shifts of H2 and H3 were assigned on the basis of 1M-decoupling experiments. Irradiation of Hi at 6 7.99 led to the collapse of the Hz resonance at 6 7.45 from a doublet of triplets to a double of' doublets ( J = 7 , s Hz, 9'= 1.5 Hz) while the H3 resonance at 6 7.73 collapsed from a doublet of triplets to a
H4 sa, R , = H
b, R , = CH,
triplet ( J = 7.5 Hz). la undergoes bisdecarbonylation slowly at 25' in acetone to give high yields of 2a. Pyrolysis of neat l a at 90' on a vacuum line gave a 95% yield of 2a and a 124% yield of GO based upon 2 mol of C!O/mol of h The infrared spectrum of 2a (Table I) contains a band at 1610 cm-1 due to the coordinated ester group (shifted from 1728 cm-1 for the uncoordinated ester of %a)and three strong CO bands due to the Mn(CQ)4 moiety. In the related compound 4, Booth has observed the coordinated ester carbonyl frequency at 1591 cm-1 . l b In the 100-MHz nmr spectrum of 2a, the chemical shifts of the four aromatic protons were widely separated and first-order splitting patterns were observed (Figure 1 and Table II). The assignment of chemical shifts was simplified since Kaesz has recently reported the nmr spectrum of' a series of related compounds, including 5sa and 5 pyrolysis of CH3Mn(CO)s in the presence of substituted acetophenones.la The chemical shift of H4 moves downfieid from 6 7.24 in la to 6 7.96 in %adue to the deshielding effect of the neighboring Mn atom in 2%.A cornparison of the mass spectra of 1%and 2%clearly indicates the conversion from an
Inorganic Chemistry, Vol. 14, No. 4, I975 797
o-Carbomethoxybenzoylpentacarbonylmanganese(1)
zso
8.00
zoos
Figure 1. Aromatic region of 100-MHz 'H nmr spectra of l a and 2a in acetone-d,. Table 11. 100-MHz Nmr Spectra
(6)
Other resonances
Compd 1aa
HI 7.93 ddd
H, 7.42 td
H3 1.71 td
7.16 ddd
3.89 (s) OCH,
1ba
7.89 dd
7.37 td
7.66 td
7.24 dd
2aa
7.15 ddd
7.19 td
7.50 td
7.94 ddd
0.87 (t, J = 8.0 Hz) CH,CH, 1.36 (q, J = 8.0 Hz) CH,CH, 3.84 (s) OCH, 4.46 (d, JP-H= 5.0 Hz) OCH, 4.08 (s) OCH,
2ba
7.53 ddd
6.96 tt
1.24 td
7.86 dddd
sab
7.83 dd
7.11 td
7.41 td
8.09 dd
5bC 3
1.13 6.94 Multiplet (ea. 7.2)
a Recorded in acetone-d,.
H,
0.76 (t, J = 7.5 Hz) CH,CH, 1.21 (q, J = 7.5 Hz) CH,CH, 3.91 (s) OCH, 4.1 1 (d, J p - ~ - = 4 . 5 Hz) OCH, 2.6 (s)COCH,
7.90
Coupling constants, Hz J,, = 1.7, J , , = 1.4, J , , = 0.5, J,,_ - = 7.5, J;; = 1.5, J,, = 7.6
J , , = 8.0, J , , = 1.O, J,, = 7.8, J,, = 1.5, J,, = 7.8 J , , = 1.6, J , , = 1.5, J , , = 0.6, J,, = 7.5, J,, = 1.2, J,, = 7.3 J , , = 7.5, J , , = 1.5, J , , = 0.6, J,, = 7.2, J,, = 1.2, J,, = 7.2, J P - H , = 1.3, JP-H, =: 1.8 J,, = 7.5, J,, = 1.5, J , , = 0.7, J,, = 7.0, J,, = 1.1, J,, = 7.0 J , , = 7.7, J,, = 1.5
1.21 (septet, J = 7.0 Hz) 3.06 (d, J = 7.0 Hz)
Reference l a .
H. D. Kaesz, private communication.
aroylmanganese compound to an arylmanganese compound since the peak due to ion 6 (m/e 163) which is 62% of the base peak in la is conspicuously absent (
