Below is one justified classification that relies on four key quantitative parameters taken from the PubChem data: the total polar surface area (TPSA), molecular weight, calculated lipophilicity (xLogP), and rotatable bond count.

When you examine the four candidate phosphane ligands, you note that two have no oxygen‐bound substituents (TPSA = 0) while the other two include two methoxy groups (TPSA = 18.5). In addition, the “non‐oxygenated” species have lower molecular weights and slightly lower calculated lipophilicity compared with the “dimethoxy” species. In short, the quantitative data provide a clear basis for two groups:

─────────────────────────────  
Group 1 (“Non‐dioxo” Phosphanes – TPSA = 0):  
• ditert‐butyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane  
  – Molecular weight ~424.6 g/mol, xLogP = 8.5, rotatable bonds = 7  
• dicyclohexyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane  
  – Molecular weight ~476.7 g/mol, xLogP = 10.1, rotatable bonds = 7  
─────────────────────────────  
Group 2 (“Dimethoxy” Phosphanes – TPSA = 18.5):  
• ditert‐butyl-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane  
  – Molecular weight ~484.7 g/mol, xLogP = 8.4, rotatable bonds = 9  
• bis(1-adamantyl)-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane  
  – Molecular weight ~640.9 g/mol, xLogP = 11.8, rotatable bonds = 9  
─────────────────────────────  

Rationale based on quantitative “database‐style” data:  
– TPSA differentiates the ligands with no hydrogen‐bond acceptors (Group 1) from those bearing two methoxy groups (Group 2).  
– Molecular weight and xLogP differences support the idea that the adamantyl/dicyclohexyl groups produce higher lipophilicity and bulk.  
– The rotatable bond count (7 vs. 9) is consistent with the extra flexibility afforded by the dimethoxy substituents.

Because these criteria come directly from quantitative values one would expect to find in a physicochemical property database, this classification into two groups is both data‐driven and in line with the “no more than three groups” requirement.