Metal BetaKetoenolate Stereochemistry - ACS Publications

37 Metal Beta—Ketoenolate Stereochemistry

Downloaded by KTH ROYAL INST OF TECHNOLOGY on September 12, 2015 | http://pubs.acs.org Publication Date: January 1, 1967 | doi: 10.1021/ba-1967-0062.ch037

J O H N P. F A C K L E R , J R . Department of Chemistry, Case Institute of Technology, Cleveland, Ohio The β-ketoenols form coordination compounds with virtually every metal and metalloid in the periodic table. The stereochemistry of these compounds is quite varied. Four-coordinate species may have either a planar or a tetrahedral idealized stereochemistry. Only octahedral tris complexes have been recognized, but both dodecahedral and square anti-prismatic tetrakis species have been studied. Some metals bond to the β-ketoenol through a carbon atom. Polymerization occurs when the coordina tion number of the metal ion exceeds twice its charge if the β-ketoenolate anion does not interfere sterically. Only a limited number of gross stereochemical arrangements are permitted for transition-metal β-ketoenolate polymers, provided they are formed by a sharing of octahedral edges or faces. On

this occasion of the one-hundredth birthday anniversary of Alfred Werner it is appropriate that the stereochemistry of metal 0-ketoenolates, especially the complexes of acetylacetone (Figure 1), should be discussed. Only within the past few years has the solution to an interest ing problem i n 0-ketoenolate stereochemistry, to which Werner addressed himself, finally appeared. I n 1901 he attempted to understand (36) the structure of certain "peculiar" (merkwurdigen) platinum(II) acetylacetonates of stoichiometry P t C l K - 2 C H ( C O C H ) and P t C l N a [ C H ( C O C H ) ] . H e also was fascinated by the metal acetylacetonates 3

3

2

2

2

H"C H X

/CH

N

2

II 0 Figure 1.

/C-H if H 0

Acetylacetone

580 In Werner Centennial; Kauffman, G.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

2

2

37.

PACKLER

581

0-Ketoenols

generally, especially because these compounds are soluble i n organic sol vents and also because of their considerable volatility. I n his 1901 paper he correctly formulated the species K P t C l ( A A ) , which contains both acetylacetonate (AA) oxygen atoms bonded to the platinum. This paper summarizes the gross stereochemical features which now have been found for /3-ketoenolato complexes, placing particular emphasis on those aspects which are most interesting. Downloaded by KTH ROYAL INST OF TECHNOLOGY on September 12, 2015 | http://pubs.acs.org Publication Date: January 1, 1967 | doi: 10.1021/ba-1967-0062.ch037

2

Coordination

to the

p-Ketoenol

There are four different ways i n which a 0-ketoenolate anion may func tion as a ligand i n bonding to metals and metalloids. These are indicated in Figure 2. B y far the most commonly found (18) coordination is through the two oxygens of the ligand. However, the coordination through the a-carbon atoms has been established conclusively by x-ray crystallographic methods for a platinum (IV) complex (34) and for the Werner complex,

Figure 2.

Acetylacetone as a ligand

K P t ( A A ) C l (21) (Figure 3). Recently, silver ions were shown by crystal lographic techniques (35) to bond (2.34 A.) with the methylene carbon i n the interesting compound, A g N i ( A A ) - 2 A g N 0 H 0 , first prepared by Ginsberg at Ohio University (22, 27). The silver perchlorate adduct of copper(II) acetylacetonate, C u ( A A ) - 2 A g C 1 0 (22), presumably also con tains silver ions bonded to the methylene carbon atom of the acetylace tonate units. Some interesting rhodium (I) complexes (28) also are thought to contain a carbon-metal bond. Bonding of the metal ion to the carbon-carbon double bond of the enol is not crystallographically established as yet, but the elegant work of J . Lewis and co-workers (1, 23, 24) has proved beyond doubt that a platinum (Il)-olefin bond exists in the acidified Werner complex, H P t ( A A ) C l (Figure 4). 2

3

2

3

2

4

2

In Werner Centennial; Kauffman, G.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.


582

WERNER

Monomeric

Figure 8.

[Me Pt(A)}

Figure 4.

HPt(AA) Cl

3

CENTENNIAL

2

2

Complexes

Since the oxygen atoms as well as the alpha carbon on the /3-ketoenolate ring can function as bases to coordinate with metal ions (3, 4, or to hydrogen bonding solvents (14) it should be recognized that /3-ketoenolate complexes may have a stereochemistry quite different from that expected—based on the stoichiometry of the complex. However, by a suitable choice of a 0-ketoenol ligand, such as 2,2,6,6-tetramethyl-3,5heptanedione (dipivaloylmethane), H - D P M , intermolecular effects can be reduced or eliminated with the result that the metal complex formed has the stereochemistry "expected" for the monomeric acetylacetonate com plex of that metal ion. For example, nickel(II) acetylacetonate is trimeric as a solid and i n solution (11), but the dipivaloylmethane complex is a monomeric, undoubtedly planar species, in solution, as well as in the solid state (37). This stereochemistry occurs with the monomeric acetyl acetonate in dilute solution or in the vapor phase, as indicated by absorption spectra and electron diffraction (30). }


37.

583

0-Ketoenols

FACKLER

Four-coordinate monomeric complexes are formed with either tetrahedral or planar stereochemistries. W i t h acetylacetone, the beryllium compound (2) has been studied crystallographically and has the expected tetrahedral configuration. Crystalline C u ( A A ) shows a nearly planar (13) arrangement; however, some intermolecular perturbation does occur. In solution, the monomer of anhydrous C o ( A A ) apparently is tetra hedral (12). It is reasonable to expect that the monomeric 0-ketoenolate complexes of the alkali earth metals as well as manganese(II), iron(II), zinc (II), cadmium (II), and lead (II) also will be tetrahedral (18). H o w ever, i n the solid state the manganese (II), iron(II) (19). and zinc (II) (6) complexes with acetylacetone apparently are polymerized (18). The cation B ( A A ) very likely also contains a tetrahedral B 0 unit. W i t h dipivaloylmethane, the zinc(II), cobalt(II) (12), and iron(II) complexes (19) are all isomorphous. A three-dimensional x-ray structural determination (12) of the C o ( D P M ) shows a tetrahedral configuration. The copper (II) complex of this ligand and the nickel (II) derivative are planar. The 3-phenyl-2,4-pentanedione derivative of copper(II) also is planar (7). Monomeric 6-coordinate complexes with trivalent metals appear a l ways to have a nearly octahedral coordination of oxygens about the metal. Structural work has shown this for A1(AA) (34), F e ( A A ) (29), C r ( A A ) (25), M n ( A A ) (26), and R h ( A A ) (31). The only case that is surpris ing is that of manganese (III) which should have a E ground state sus ceptible to Jahn-Teller removal of degeneracy. The x-ray data for M n ( A A ) , which shows six nearly equal M n - 0 bond lengths, are not con sistent with electronic spectral data available for the 0-ketoenolate com plexes of manganese (III). The x-ray data possibly may be re-interpreted in terms of a random disordering (18) of tetragonally distorted M n ( A A ) units i n the crystal. N o trigonal prismatic structure is known with /3-ketoenolate ligands In A g N i ( A A ) - 2 A g N 0 H 0 , the anionic N i ( A A ) ~ contains (35) a nearly octahedral Ni(>6 unit. The anionic tris complexes of magnesium(II), zinc (II), cadmium (II), cobalt (II), and manganese (II) presumably also have a similar stereochemistry, although no structural work is available. The cationic silicon (IV), germanium (IV), and titanium (IV) tris complexes also probably are octahedral; however, this has been proved only for S i ( A A ) which has yielded optical isomers (15). Four 0-ketoenolate ligands about a metal ion produce 8-coordinate complexes i n which an anti-prismatic or a dodecahedral arrangement of oxygens about the metal ions is found. The Z r ( A A ) complex is known crystallographically (32) to have the ~ D symmetry of the Archimedean square anti-prism. Hafnium complexes also are similar, as is the /? form of T h ( A A ) and P u ( A A ) (16). The a form of T h ( A A ) and that of C e ( A A ) and U ( A A ) may be considered somewhat distorted dodecahedra 2


2

2

+

4

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h

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+

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WERNER

CENTENNIAL


(32). (See paper by M a t k o v i c and Grdenic (24a).) The esthetically i n teresting "pinwheel" structure based on the anti-prism, Figure 5, has not been found and, according to Silverton and Hoard (32), is not likely to be found.

Figure 5.

"Pinwheel"

structure

Tetrakis anionic complexes have been isolated with certain lanthanides, such as E u ( I I I ) , Tb(III), and Gd(III). The structure of the complex, ( N H ) E u ( F A A ) 4 , H F A A = l,l,l-trifluoro-2,4-pentanedione, has been completed recently (31), but the complete data for the 8-coordinate species are not yet available. 4

3

3

Excluding cases where the complex interacts strongly with solvents or with itself, solution spectroscopic data generally have corresponded well with structural data, except as indicated for M n ( A A ) . The tris chelate complexes of the transition elements appear to remain approximately octahedral i n solution. In fact, F a y and Piper (20) showed conclusively by N M R and optical activity studies that the trigonal prismatic configura tion is not even an intermediate in the isomerization of the unsymmetrical M ( A ) complexes of A l ( I I I ) , Ga(III), and Cr(III). 3

3

Polymeric Complexes When the coordinating ability of the metal ion is not satiated by the 0-ketoenol ligands—i.e., the coordination number exceeds twice the charge, and if the ligands sterically allow it, polymerization (or adduct formation) of the neutral /3-ketoenolate complex occurs. Crystallographic evidence is available for the species [ N i ( A A ) ] (6), [Co(AA) ]4 (9), and [ ( C H ) P t ( A ) ] (33), while there is also good evidence for polymerization with M n ( A A ) , F e ( A A ) , L n ( A A ) L n = lanthanides), U 0 ( A A ) , and R T 1 ( A A ) (18). The degree of polymerization is variable and, in solution, the species [ M n ( A A ) ] , [Fe(AA) ] , [Ln(AA) ] , [ U 0 ( A A ) ] , and 2

3

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6

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FACKLER

585

p-Ketoenols

[R T1(AA)] have been suggested. Z n ( A A ) appears to crystallize as a trimer (3, 4, 5), and C r ( A A ) (18) also appears to be polymeric. Three basic ways exist i n which a neutral M ( A A ) species may poly merize (ignoring specific ring orientations). Two involve using the oxy gens, and one, the a-carbon atom pictured in Figure 6. Crystallographic evidence exists for the oxygen bonding, as i n 6a, and the carbon bonding, 6c, while spectroscopic data were presented by Colton et al. (8) for the bridges pictured i n 6b for the compound R e ( A A ) C l . 2

2

2

2

n


2

Figure 6.

4

4

Polymer structures

For polymers of type 6a, octahedra may be joined by faces or by edges, or both, as i n [Co(AA) ] , shown in Figure 7. If one assumes (a) that each metal ion is surrounded by an octahedron of oxygens, and (b) that poly merization can occur only by joining octahedral faces or edges (points also might be used, but the relative strength of the association would be reduced considerably), it can be shown that up through six M ( A A ) units, only one formal structure has reasonable stability (Table I). (The "formal" structure ignores specific cis-trans arrangements. A s Cotton and Elder showed (10), there are nine possible trimeric [ N i ( A A ) ] structures involving shared octahedral faces.) For N, the number of metal atoms equal to five and six the formalistic structures pictured in Figure 8, is pre2

4

2

2

3



WERNER CENTENNIAL


37.

587

p-Ketoenols

FACKLER

dieted. Unfortunately, the most likely value of N cannot dicted for the polymeric units. I n fact, little differences expected between certain polymeric forms; hence, it may find variable polymerization numbers for these species crystallization conditions. Table I.

as yet be pre i n energy are be possible to depending on

Possible Numbers of Face (F) and Edge (E) Oxygen Atoms for Polymeric, Octahedral /?-Ketoenolates


a

N

0

Sites

2 3 3 4 4 5 5 6 6 6

8 12 12 16 16 20 20 24 24 24

12 18 18 24 24 30 30 36 36 36

F

E

Comment

0 6 0 0 6 0 6 12 0 6

4 0 6 8 2 10 4 0 12 6

Impossible Found Impossible Impossible Found Cyclic Likely Impossible Cyclic Likely

° F + E + P = 0, P = points, N = No. of metal atoms 2F + 2E + P = S, S - sites = 6JV Thus F + E - S - 0 and 20 - S - P, F - 0, 3, 6, 9 . . ., E - 0, 2, 4, 6 . . . . Starred species may contain the octahedral face bonded dimenc unit described by Fackler (17) and found in [Co(AA) ] and [Ni(AA) ] . Cyclic structures are not expected. 6

2

Hetero-atom

4

2

3

Complexes

Some very interesting structural features exist for neutral 0-ketoenolate complexes (18) of the type M ( A A ) L . Adducts with nitrogenous bases or water have yielded a 5-coordinate irregular Z n ( A A ) - H 0 complex and trans 6-coordinate cobalt (II) and nickel (II) complexes M ( A A ) - 2 B , with B = H 0 or pyridine. The vanadyl complex, V O ( A A ) , contains a square pyramid of oxygens about the metal, while U 0 ( A A ) H 0 shows a pentagonal bipyramidal structure. The anhydrous material is dimeric. Besides Z n ( A A ) - H 0 , ostensibly 5-coordinate species are known with C u ( A A ) - B and C o ( A A ) - B . The cobalt(II) compound with water exists as a dimer containing octahedra which share an edge; however, spectroscopic evidence indicates that a monomeric 5-coordinate adduct can be formed under suitable conditions. Bases generally give a 5-coor dinate adduct with C u ( A A ) , although C u ( F A A ) - 2 H 0 presumably is 6-coordinate. M u c h additional material could be written about the stereochem istry of jS-ketoenolate complexes containing hetero-atoms, particularly with regard to organometallic compounds such as ( C H ) A u ( A A ) or n

m

2

2

2

2

2

2

2

2

2

2

2

2

6

2

2

3

2


2

588

WERNER CENTENNIAL

(CH )2Sn(AA) . However, significant information currently is being obtained i n this area, so that a review of this subject will be more appropriate at a later date. 2

3


Acknowledgments I wish publicly to thank E . C. Lingafelter for helpful information in writing this review. Also, I wish to thank the National Science Founda tion, GP-4253, the Public Health Service, and the Petroleum Research Fund for financial support.

Literature

Cited

(1) Allen, G., Lewis, J . , Long, R. F., Oldham, C., Nature 202, 590 (1964). (2) Amirthalingam, V., Padmanabhan, V . M., Shankar, J . , Acta Cryst. 13, 201 (1960). (3) Bullen, G. J., Nature 177, 537 (1956). (4) Bullen, G. J . , Mason, R., Pauling, P. J . , Nature 189, 291 (1961). (5) Bullen, G. J . , Mason, R., Pauling, P. J . , Inorg. Chem. 4, 456 (1965). (6) Bullen, G. J., Mason, R., Pauling, P., Inorg. Chem. 4, 456 (1965). (7) Carmichael, J. W., Jr., Steinrauf, L . K . , Belford, R. L., J. Chem. Phys. 43, 3959 (1965). (8) Colton, R., Levitus, R., Wilkinson, G., Nature 186, 233 (1960). (9) Cotton, F. A., Elder, R. C., J. Am. Chem. Soc. 86, 2294 (1964). (10) Cotton, F. A., Elder, R. C., Inorg. Chem. 4, 1150 (1965). (11) Cotton, F. A., Fackler, J. P., Jr., J. Am. Chem. Soc. 83, 2818 (1961). (12) Cotton, F. A., Soderberg, R. H . , J. Am. Chem. Soc. 84, 872 (1962). (13) Dahl, L., Mol. Phys. 5, 169 (1962). (14) Davis, T. S., Fackler, J. P., Jr., Inorg. Chem. 5, 242 (1966). (15) Dhar, S. K., Doron, V., Kirschner, S., J. Am. Chem. Soc. 80, 753 (1958). (16) Dixon, J. S., Smith, C., Nat. Nucl. Energy Ser., Div. IV, 14B. Transuranium elements Pt, 855 (1949). C A 44: 3388 (1950). (17) Fackler, J. P., Jr., J. Am. Chem. Soc. 84, 24 (1962). h

(18) Fackler, J. P., Jr., Progr. Inorg. Chem. 7, 361 (1966).

(19) Fackler, J. P., Jr., Holah, D . G., Buckingham, D . A., Henry, J. T., Inorg. Chem. 4, 920 (1965). (20) Fay, R. C., Piper, T. S., Inorg. Chem. 3, 348 (1964). (21) Figgis, B. N., Lewis, J . , Long, R. P., Mason, R., Nyholm, R. S., Pauling, P. J . , Robertson, G . B., Nature 195, 1278 (1962). (22) Ginsberg, C. S., Ph.D. Thesis, Ohio Univ., 1964; Univ. Microfilms 64-10, 595. (23) Johnson, B. G., Lewis, J., Subramanian, M. S., Chem. Commun. 1966, 117. (24) Lewis, J . , Long, R. F., Oldham, C., J. Chem. Soc. 1965, 6740. (24a) Matkovic, B., Grdenic, D., Acta Cryst. 16, 456 (1963). (25) Morosin, B., Acta Cryst. 19, 131 (1965). (26) Morosin, B., Brathovde, J. R., Acta Cryst. 17, 705 (1964). (27) Oestreich, C. H . , Ph.D. Thesis, Ohio Univ., 1961; Univ. Microfilms 61-5688. (28) Parshall, G. W., Jones, F. N . , J. Am. Chem. Soc. 87, 5356 (1965). (29) Roof, R. B., Acta Cryst. 9, 781 (1956). (30) Shibata, S., Bull. Chem. Soc. Japan 30, 753 (1957).

(31) Sicker, M. L., private communication from E . C. Lingafelter. (32) Silverton, J. V., Hoard, J. L., Inorg. Chem. 2, 243 (1963). (33) Swallow, A . G., Truter, M. R., Proc. Roy. Soc. (London), 254, 205 (1960).


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FACKLER

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(34) Shugam, E . A., Shkol'nikova, Doklady Akad. Nauk SSSR 133, 386 (1960); Trans. 133, 811 (1960). (35) Watson, W. H., Jr., L i n , Chi-Tsun, Inorg. Chem. 5, 1074 (1966). (36) Werner, A., Ber. 34, 2584 (1901).

(37) Wise, J . , Ph. D. Thesis, Massachusetts Institute of Technology, 1965.


RECEIVED June 28, 1966.


Metal BetaKetoenolate Stereochemistry - ACS Publications

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