κ¹- and κ²-Complexes of Fluorenylidene–Allenyl Phosphines and Phosphine Oxides with Palladium Chloride and Iron Carbonyl: Displacement of Trimethylsilyl by Diphenylphosphino via a Stabilized Carbanion

An attempt to prepare 3,3-(biphenyl-2,2′-diyl)-1-diphenylphosphino-1-(trimethylsilyl)allene, <b>15</b>, by treatment of 3,3-(biphenyl-2,2′-diyl)-1-lithio-1-(trimethylsilyl)allene with chlorodiphenylphosphine led instead to 3,3-(biphenyl-2,2′-diyl)-1,1-bis(diphenylphosphino)allene, <b>14</b>. The proposed mechanism invokes attack on the trimethylsilyl group in <b>15</b> by liberated chloride to form a stabilized anion that reacts with a second molecule of the chlorophosphine. The diphosphine, <b>14</b>, reacts with di-iron nonacarbonyl to form monodentate <b>14</b>-Fe(CO)₄ and the chelate <b>14</b>-Fe(CO)₃. 9-Ethynyl-9<i>H</i>-fluoren-9-ol and chlorodiphenylphosphine form 3,3-(biphenyl-2,2′-diyl)-1-diphenylphosphinylallene, which is readily deprotonated by triethylamine to generate a stabilized fluorenyl anion, which reacts with a second molecule of the chlorophosphine to furnish 3,3-(biphenyl-2,2′-diyl)-1-diphenylphosphino-1-diphenylphosphinylallene, <b>26</b>. This bis-phosphine-monoxide (BPMO) reacts with di-iron nonacarbonyl to form initially monodentate P-bonded <b>26</b>-Fe(CO)₄, which loses a carbonyl, allowing the adjacent allene double bond in <b>26</b>-Fe(CO)₃ to coordinate to iron and leave the phosphine oxide uncoordinated. In contrast, the BPMO, <b>26</b>, and (PhCN)₂PdCl₂ yield the phosphine-coordinated, chlorine-bridged dimer <b>34</b> and also the chelate <b>35</b>, in which the palladium is linked to both the diphenylphosphino and diphenylphosphinyl groups via phosphorus and oxygen, respectively. Surprisingly, chlorodiphenylphosphine and 1,4-bis(9-hydroxy-9<i>H</i>-fluorenyl)buta-1,3-diyne, <b>37</b>, do not yield the expected 3,4-bis(phosphinyl)hexa-1,2,4,5-tetraene, <b>33</b>, but rather the 1-chloro-2-diphenylphosphinocyclobutene, <b>38</b>, bearing a spiro-bonded fluorenylidene and a fluorenylidene-allene. All new compounds were characterized by ³¹P NMR spectroscopy and X-ray crystallography.