The com
plexes
cis-[PdCl
2{η
p>2p>-[C(H)PH
3]
2CO}] (
2) in two different stereochemical arrangements (cisoid–cisoid,
2cc; cisoid–transoid,
2ct) have been studied by DFT methods at the B3LYP level. The (
2cc) structure is energetically more stable than the (
2ct), being the main res
ponsible of the energy difference between the two com
plexes the energetic ga
p between the
cc and
ct isomers of the free bis-ylide ligand [H
3P
![](/images/gly<font)
phs/BPQ.GIF>C(H)–C(O)–C(H)
![](/images/gly<font)
phs/BPQ.GIF>PH
3] (
1). In (
1) these differences arise from the
presence of 1,4-intramolecular interactions between the
phos
phorus atoms and the carbonyl oxygen. That is, the conformational
preferences observed in (
1) due to the establishment of 1,4-P
phs/BN9.GIF>O interactions are directly transferred to the metallic com
plexes (
2) in such a way that the most stable structure for the free ligand gives the most stable com
plex. In the absence of the carbonyl grou
p (e.g. [H
3P
![](/images/gly<font)
phs/BPQ.GIF>C(H)–C(
![](/images/gly<font)
phs/BPQ.GIF>CH
2)–C(H)
![](/images/gly<font)
phs/BPQ.GIF>PH
3] (
3) or [H
3P
![](/images/gly<font)
phs/BPQ.GIF>C(H)–CH
2–C(H)
![](/images/gly<font)
phs/BPQ.GIF>PH
3] (
5)) all isomers of a given bis-ylide (
cc,
ct and
tt) become isoenergetic. The absence of discrimination in the free bis-ylides (
3) and (
5) gives isoenergetic
cc and
ct structures for the corres
ponding com
plexes
cis-[PdCl
2{η
p>2p>-[C(H)PH
3]
2C
![](/images/gly<font)
phs/BPQ.GIF>CH
2}] (
4),
cis-[PdCl
2{η
p>2p>-[C(H)PH
3]
2CH
2}] (
6) and [C
pNi{η
p>2p>-[C(H)PH
3]
2CH
2}] (
7), as stated by NMR s
pectrosco
py for (
7). The influence of other factors (change of the heteroatom at C
β, change of the P substituents) in the energy of the different isomers of the bis-ylides and in the energy of the corres
ponding com
plexes has also been studied and discussed.